The Stage of Rivers of Blood and Mountains of Corpses: Shimosa (屍山血河舞台 下総国, Shizan Ketsuga Butai?, localized as "The Stage of Carnage: Shimousa"), Tournament of the Seven Blade-Master Heroic Spirits (英霊剣豪七番勝負, Eirei Kengou Nanaban Shoubu?, localized as "Seven Duels of Swordmasters"), is Subspecies Singularity III (亜種特異点 III, Ashu Tokuiten III?, localized as "Pseudo Singlarity III"), or more properly Subspecies Parallel World (亜種並行世界, localized as "Pseudo Parallel World"?), of the Remnant Order dealing with the aftermath of the Human Order Incineration Incident in Fate/Grand Order. It occurred in the Shimosa province of Japan in A.D. 1630 (Kan'ei 16).
Although initially designated as a Singularity and bearing considerable similarities to one, Shimosa is not a proper Singularity in the sense of the Human Order. Described as an otherworld (異界, Ikai?) and subsequently designated as a Subspecies Parallel World, it is a timeline which exists between dreams and reality, distinct enough that it should be designated for culling but hasn't been. Due to its isolated nature, the Counter Force is apparently somewhat weaker there, though as it is not within the standard Tree of Time (but at the same time, not within another universe), the events within should not be able to threaten the Tree.
The interior is comprised of the Shimosa province of Japan in the year 1630 during the early part of the Edo period. Unlike the normal world, its capital city is built around the Castle of Toke and the Matsudaira clan resides in the castle.
A parallel version of Amakusa Shirou Tokisada, who survived the Shimabara Rebellion in a culled world, travelled across many worlds after becoming a Mobile Singularity. His hatred for the Tokugawa grew, as he saw they repeated their massacre of christians at Shimabara across several worlds. His hatred changed him into something beyond human. He then began searching for a world where Matsudaira's daughter is living near Edo following the Shimabara Rebellion when Satan directs him to Shimosa. They also grant him a portion of its power. He met Ashiya Douman at Shimosa, while the latter was searching for information for the missing history under the directions of the God of a Distant Star. Douman instructs him in a ritual that could achieve his goal, comparing it to the Holy Grail War. At Katori Shrine, Amakusa Shirou summoned Tomoe Gozen, Minamoto no Raikou, Shuten-douji, Mochizuki Chiyome, and Hōzōin Inshun with the Holy Grail. Douman then infused them with the Curse of Annihilation to turn them into Heroic Spirit Swordmasters with unintended expection of Inshun. The curse transforms them into immortal creatures driven by hatred and a intense desire to kill. Yagyū Munenori joins them despite being human for a chance to duel Miyamoto Musashi again. They are instructed by Amakusa Shirou to kill everyone in Shimosa. Both their souls and the grieving souls of those they slaughter will serve as the foundation of Onriedo Castle. Once it is constructed, Amakusa Shirou will sacrifice one of Tokugawa blood to it. The sacrifice will serve as the perfect catalyst to cast a far-ranging multilayered curse on the Tokugawa regime. This will destroy any possible world where the Tokugawa exists. Considering Amakusa Shirou a threat, the Counter Force summoned Sengo Muramasa to Shimosa to stop him a month before Musashi and Ritsuka's arrival. When Musashi arrived in Shimosa, her and Amakusa Shirou's natures as Mobile Singularities caused a number of abnormalities and unusual phenomena to occur. These include monsters that Amakusa Shirou and the Swordmasters took control of.
As opposed to entering via rayshifting, Ritsuka Fujimaru was transported inside via dreams.
Ritsuka recalls to Mash and Sasaki Kojirou their meeting with a female Musashi in a dream-like experience. Mash deduces this Musashi was from a culled parallel world, and she was travelling between worlds through special means. She correctly assumes she is a living person rather than a Heroic Spirit. Unlike the male Musashi of their history, the female Musashi has yet to reach the pinnacle of her swordmanship, she never dueled Saski, and she never wrote the Book of Five Rings written by the male Musashi of their history. However, as Saski utter Musashi's other name: Shinmen Musashi no Kami Fujiwara no Harunobu, Ritsuka sees visions of a countryside and a burning building. They then collapse and goes into a coma.
Ritsuka wake up in a field, having been caught earlier by Miyamoto Musashi. She assume they're experiencing a rare case of travelling to another world through their dreams. She guesses Ritsuka is likely dreaming while simultaneously the current world truly exists. Thus if they die before waking up, they will die in reality. Musashi then reveals she cannot return to worlds she previously visited. She decides to help Ritsuka return to reality, so she can continue her journey.
While searching for a village, the pair encounter a young girl carrying a baby, Onui and Tasuke. They learn from Onui that they're in Shimosa, and the current ruler is Iemitsu Tokugawa is the current ruler. All of this differs from the Japan Musashi knows. Onui then invites Ritsuka and Musashi to her grandpa's hermitage. However, the sky suddenly darkens, and the group are beset by spirits. After the spirits are destroyed, the sky returns to normal. Onui assumes they were bandits since Musashi was able to slay them without being a monk, but Ritsuka and Musashi disagree.
As the group travel to her grandpa's hermitage, Onui says the spirits don't appear in there or the village, even at night. The sky then darkens again, but the spirits are quickly slain by Hōzōin Inshun with a single strike of his spear. He was summoned alone two days ago at Katori Shrine. He left the shrine after having a terrifying premonition, wandering and slaying the spirits that appeared. He assumes someone is using a Holy Grail to summon the spirits.
At Katori Shrine, a sorcerer declares the dark Jesuit sorcery he performed there has granted them control of seven Heroic Spirits. He says they're not Heroic Spirits, but Heroic Spirit Swordmasters made to destroy the world. Caster of Limbo concurs, stating how he and other Heroic Spirits were summoned by the Grail and infused with his Curse of Annihilation. He explains the Swordmasters will obey the sorcerer's commands, declaring they cannot be hurt or killed by any blade. They will kill all in their path until every human is dead. Caster notes they're missing one though, which the sorcerer is aware of. He then order Caster to turn day into night.
Meanwhile with the group, day turns into night occupied by a blood moon. Sensing there will be greater danger than before, they hurry eastward to the children's home. They try to cut through a bamboo forest when they encounter the Swordmasters. Inshun tries to attack one , only for Archer to deflect him with an arrow. Caster then appears and declares the Swordmasters materialized to turn the world into a hell. Musashi slashes away the fire that suddenly attacked her, and seemingly thwarts Assassin of Parasio's ambush, though it was only an afterimage. She then attacks Rider of Kālasūtra Hell aided by her Heavenly Eye, but her attack is blocked. Berserker of Saṃghāta Hell unleashes a wave of her special brew said to melt bodies, but Inshun deflects it with Hazy Inverted Moon - Eleven Styles. A cold-blooded swordsman, who Musashi assumes to be the leader, then appears. He demands Inshun to be handed over, stating everyone will be massacred afterwards. Inshun holds the Swordmasters off while the others escape. He then fights the swordsman with the aid of his Noble Phantasm. He eventually pierces his heart, but finds he cannot move his spear. The swordsman reveals such attacks would kill a human or Heroic Spirit, and introduces his Cursed Name as Saber of Empireo. Caster casts the Curse of Annihilation on Inshun on Saber's command. He reveals Inshun was summoned to serve as the seventh Swordmaster, but he was summoned with free will unlike the others.
The group continue escaping when they encounter Inshun. However he is now a Swordmaster, the Lancer of Purgatorio. Musashi decapitates him during the ensuing fight to protect the children, but he gets up and reattaches his head. The group escape to the village, and hide in a nearby haystack. Inshun tries to antagonize Musashi by massacring the village. The group then leave the haystack and head for the hermitage.
At the hermitage, the group meet Onui and Tasuke's grandpa, though he's a young man. Inshun arrives and attacks him, but he dodges and destroy Inshun's body with a single blow. Inshun regenerates and boasts there isn't any technique nor blade that reach the Spiritual Core of a Swordmaster. After regenerating from another attack, he reveals he massacred the villages lying to the north and west. He claims his body is now a puppet controlled by karma, so the only way to stop him is his complete destruction. Musashi takes the sword Onui and Tasuke's grandpa recently made, feeling a divine aura from it. He considers it a fail, saying it can effortlessly cut through anything, but he pushed it into the realm of demons. Musashi then challenges Inshun to a duel to reach the apex of her mastery. Inshun responds by casting a spell similar to a reality marble, a field of corpses where the loser's soul will be consumed. Thanks to the sword she took earlier, Musashi was able to reach Inshun's Spiritual Core and kill him. The group then go into the hermitage.
Inside the hermitage, Musashi keeps the sword as an exception to her rule of four. Onui and Tasuke's grandpa explains it is a failure since it is an evil blade that reached the realm of demons. The ultimate blade he seeks isn't one that cuts flesh and bone, but one that can severs bonds, certainty, and karma. Musashi realizes she freed Inshun from his karma thanks to the sword. Onui and Tasuke's grandpa still considers it failure though since it cannot cut bonds or certainty. He then dubs it Myoujingri Muramasa, revealing himself to be Senji Muramasa.
Later, Muramasa reveals he is a Rogue Servant summoned near the village about a month ago. By the time he got there though, monsters had already killed half of the villager including Onui and Tasuke's parents. After taking the children in, he took the hermitage from the western village. Monsters started to appear around the time he was summoned. He recalls a rumor that the monsters are controlled by the Swordmasters. He also recalls hearing a man performing dark Jesuit sorcery at Katori Shrine. His mysticism instantly turning day into night, and summoned the Swordmasters to destroy humanity. He also heard the Swordmasters razed the Hitachi Provice. Musashi decides they need more information on the monsters and the Swordmasters. Muramasa directs them to Toke Castle Castle as a place to get more info.
Taking the children with them on Muramasa's request, Ritsuka and Musashi travel to Toke Castle Town. They ask the townsfolk about the monster, but no one takes it seriously since they almost never appear nearby. They also realize no one has heard about the village massacres yet, possibly due to the castle controlling information. Musashi also considers the possibility of them secretly gathering information on the Swordmasters and their summoner. The group eventually meet Otama, a geisha sharing Tamamo-no-Mae's appearance. Kiyohime, daughter of Lord Matsudaira Shimousa-no-Kami, then suddenly appears. She and Otama get into a violent argument over Ritsuka that Musashi is forced to break up. After Otama and Kiyohime return to their respective abodes, the group encounter a missionary who looks like Edmond Dantès. He directs the group to an alleyway where they'll meet someone they need and leaves. There they find Fuuma Kotarou collapsed, so they take him to Otama's inn.
At the inn, Kotarou explains he came to return Ritsuka to reality. However, he was the only Servant who was able to make it. He tries to explain to Ritsuka that they're in a dream they cannot wake from when he passes out again. He wakes up though after hearing Ritsuka has been summoning in battle. He believes they're temporarily borrowing the shadows of the Servant's Spirit Origins. After he falls asleep, Musashi tells Ritsuka how one can see the faces of those they know on strangers when travelling to other worlds through dreams. Otama then enters the room and allows the group to stay until Kotarou recovers.
At Katori Shrine, Caster reports that Inshun is gone, blaming it on his incomplete summoning. Saber considers Inshun a failure because he failed to take even a hundred lives. Despite that though, the Sorcerer says Inshun still served as an excellent cornerstone for the Onriedo. He calls it similar to the Holy Grail War, as the souls of Swordmasters will reside in the foundations of his Onriedo. The souls of a few Heroic Spirits are insufficient to manifest the Onriedo. Thus, more to be killed to help it grow with the souls of those drenched in bitterness, envy, and grief. That is why the Swordmasters were granted the Curse of Annihilation made from Caster's technique and the Sorcerer's power. The Sorcerer's bodyguard then enters the shrine. He is a human that the Sorcerer met in the Hitachi mountains, and brought him back to serve as his bodyguard on a whim. The Sorcerer then commands the Swordmasters to continue killing while he prepares for the arrival of the Onriedo. After he leaves, Caster orders Katou Danzo to sick Archer of Inferno on Musashi. He also orders her to closely observe a group of samurai from Edo that'll soon arrive in Toke Castle by pretending to be on a secret mission from the Shogunate. Once Caster determines everything is set, Danzo will bring Archer and Musashi together, and witness what comes next.
At the inn, Ritsuka and Musashi sneak out after she sensed a disturbance outside. They arrive outside to find evil spirits and destroy them. Musashi senses the Swordmaster who commanded them is nearby. Archer then unveils and introduces herself with her Cursed Name. She declares the Swordmasters' goal is to kill and burn related to Tokugawa society. She then starts unleashing fire, so Musashi fights her to ensure her fire doesn't spread. They're unable to best each other since Musashi can't close the distance thanks to Archer's arrows and flames, while Archer's arrows are continuously deflected by Musashi at the last moment. Musashi realizes Archer is holding back, as she has yet to use the spell Inshun used. Archer admits she was told to hold back, and vanishes with the promise of fighting Musashi in full force. Ritsuka and Musashi then return to the inn to rest.
Later, Kotarou has recovered some. The group then notice a commotion and go to investigate it. They learn a large procession of samurai has recently arrived from Edo. One of the samurai, Sakon, tells the townsfolk to be quiet and pay attention while his superior speaks. Yagyū Munenori, chief inspector for the shogunate, explains he and the other samurai are on a official mission bring the monsters (who he believes are bandits) slaughtering innocents in southern Shimousa to justice with Matsudaira's cooperation. He then confronts Musashi, recalling they dueled six months ago. Musashi finds it strange she is the same time and place from six months ago since she has never visted the same place twice before. Yagyu decides to duel her to determine her intentions when monsters fly in from the south. As another wave comes, he orders Sakon to get the townsfolk out of the vicinity. After slaying the monsters with the group, Yagyu assumes they were a scouting party. He orders Sakon to tell Matsudaira to deploy archers. He also orders to concentrate their forces to the south, believing the castle can have the bare minimum of soldiers. After the samurai leave, Ritsuka tell Yagyu their assumption that Archer is leading the monsters. Yagyu then tells the group that a hundred of his finest men will confront Archer as a diversion while they ambush her from behind. He advises them to go through the mountain pass to do so. Danzo then arrives; Yagyu explains she is the spy who saw Archer leading the monsters. She will also serve as the group's guide through the mountain pass.
As the group walk the mountain pass, Danzo confirms she is an over century old puppet animated by machinery. Kotarou confirms she is a living person from the era. The group reach their destination, and stop Archer from incinerating more samurai. Kotarou orders Danzo take the injured to safety, and give the others new orders since they cannot stand against a Servant. Musashi deduces Archer's True Name is Tomoe Gozen when she shouted Lord Yoshinaka. She then readies to fight her with Myoujingri Murasama, and Tomoe takes them both to the other plane for their duel. After she is defeated, Tomoe disappears recalling her love for Yoshinaka. With her demise, the monsters are sent into disarray. The group then help Danzo and the samurai deal with the remaining monsters.
Later, Musashi challenges Kotarou to a duel since he's fit enough for battle now. After the duel, they notice a crowd gathering around a nearby ichimai-zuri seller. The seller tells the crowd that a letter was sent to Toke Castle, threatening to assassinate Kiyohime. The group decide to head to Toke Castle, hoping Yagyu will let them in.
At Katori Shrine, Assassin reports that she has delivered the letter regarding Kiyohime's assassination to Toke Castle. By now ten of Yagyu's samurai should be guarding Kiyohime now, and rumors should also be circulating. The Sorcerer orders Assassin to assassinate Kiyohime after letting panic about her assassination to spread throughout the population. Afterwards, the populace will be instilled utterly with fear, thus their souls will be better sacrifices.
Inside Toke Castle, the group wait to meet with Kiyohime. They recall Muramasa taking the children back to his hermitage. Kiyohime soon enters the room with Yagyu. Kotarou realizes they've yet to see history distorted by the Grail. He feels something is fundamentally different about the world's foundation. Kiyohime tells the group that many were killed when the letter was delievered. Despite having the castle guards and 300 of Yagyu's samurai to protect her, she asks the group to protect her also. She then pays Musashi 30 ryou to spar with her to prove the results of her marital arts training. She then orders Danzo to fight with her after Musashi warned her not to fight her alone, even though she'll be going easy on her.
Later at night following the fight, Musashi stays with Kiyohime, while Koatoru guards Ritsuka in their room. He then senses a Swordmaster has infiltrated the castle. He and Ritsuka then arrive outside to fight Assassin after convincing the surviving warriors not to fight her. Assassin declares her master, the Sorcerer, will wield the power of Satan to sacrifice Shimosa to destroy this world created by the Tokugawa. She explains she'll assassinate Kiyohime to devastate Shimosa's people in order to make Shimosa easier to destroy. She then easily kills ten castle guards with snakes, adding her total victims to forty. She then ights Ritsuka and Kotarou. After Kotarou decapitates her, Assassin decides to stop holding back. Musashi suddenly throws Myoujingri Murasama at her, only for it to miss and be caught by Kotarou. He then blocks the kunai Assassin threw at Kiyohime, who followed Musashi outside. Musashi slashes at Assassin, only for it to be an illusion while the real one had already escaped. Danzo appears and reports that Yagyu will arrive momentarily with an assembly of his samurai. Kiyohime then faints after learning twenty castle guards were killed by Assassin.
At Katori Shrine, Caster reports Assassin and Danzo have laid the groundwork for the Onriedo. Saber responds that fear is spreading throughout Shimosa, and the great pentagram being drawn in secret via Jesuit sorcery is nearing completion. The Sorcerer tells the others that Assassin needs to be removed now that she has spread fear amongst the populace. Meanwhile in Toke Castle town, Assassin encounters Berserker. She proceeds to connect Assassin's heart and brain to power of the god of Mt. Ibuki, Orochi, that resides in her to the former's protest. She apologizes for her act, explaining the Sorcerer needs Ritsuka and Musashi eliminated.
At Toke Castle, Yagyu orders his samurai to increase security when Assassin returns and summons Orochi. Musashi and Kotarou slay it when Kiyohime suddenly attacks Ritsuka with her fire. Kotarou manages to protect them with his own body. Orochi then revives despite being reduced to ash by Kotarou's Immortal Chaos Brigade due to Assasin's Saigyou revival technique. Assassin then tells Kiyohime to kill the group, and she will kill her afterwards. Kotarou realizes the kunai Assassin threw at Kiyohime last night was merely a feint to put her under a spell. The group then fight Kiyohime and Orochi. After Orochi is slain again, Musashi deduces Assassin is Mochizuki Chiyome. Chiyome then brings them to the other plane for their duel. After Chiyome is killed, Kotarou pick up her kunai that didn't disappear with her since they were procured in Shimosa. Musashi recalls her saying something about the Onriedo, a Buddhist word for distancing oneself for this impure world and its earthly desires.
The group travel back to the hermitage, accompanied by Danzo. Her new orders from Yagyu are to gather information around Shimosa, and to ensure the group arrive safely at their destination. She then recalls Berserker collecting Orochi's remains at Toke Castle for her wine before proceeding to Arakawa. She then witnessed Rider slaughter an entire army of 10,244 men on east bank of the Arakawa River while they were en route to rendezvous with Yagyu. She only spared a young soldier left mentally broken by the slaughter, believing he'd make a poor sacrifice. She then departed for Sagami with Berserker to unleash her Noble Phantasm upon it. Danzo reminded them that they weren't ordered to do so, but they ignored her.
At the hermitage, Muramasa tell the others about what transpired near Arakawa River. The soldier who survived the massacre crossed the river, and relayed that two beautiful women were responsible before dying. The group deduce the two women are Swordmasters. Muramasa then reveals the entire Sagami Province was also destroyed. He continues the two women left Sagami, and went on a killing spree until high noon. Because they vanished by then, smaller villagers were spared, but larger places like Kamakura and Odawara Castle town were nearly massacred. The group then suddenly hear Onui screaming from outside. They rush out there to find her and Tasuke captured by Berserker and Rider. Ritsuka recognizes them as Shuten-douji and Minamoto no Raikou respectively, but they aren't the ones from Chaldea. Musashi attacks Shuten, but Raikou blocks it. The Swordmasters then overwhelm the group using only a fraction of their power. Raikou tells them to come to the peak of the nearby mountain before high noon if they wish to save the children. After they escape, the group, prepare to go to the nearest mountain.
After Muramasa forges a new sword, the group leave for the mountain. They cut through the nearby bamboo forest into a mountain trial. As they continue to ascent, Orochi suddenly appears, even though Chiyome is long gone. Kotarou realizes Shuten is able to summon it because she is a descendant of Orcohi. With the last of its energy, Orochi knocks Ritsuka down a slope. Kotarou goes to save them when another Orochi appears.
Ritsuka find themselves in a cave, having been knocked unconscious while tumbling down the mountain slope. Shuten is also there mending their ankle, having found them after Raikou kicked her off the peak. She offers Ritsuka anything they want if they join her. They want Onui and Tasuke returned, but Shuten refuses and begins tearing into their stomach. They eventually fall unconscious from the pain.
Musashi, Kotarou, Muramasa, and Danzo eventually find Ritsuka. Kotarou uses his clan's secret ointment to close their wound. After getting more rest, Ritsuka continues onward to the peak with the others. There the group confront Shuten and Raikou, and demand the children back. They doubt Shuten's claims that she ate them. They then kill the Orochi summoned by her. Afterwards, Shuten and Raikou bring Musashi to the other plane for their fight. After Shuten disappears, Raikou tells the group that the children are safe in a small shrine up ahead. She confirms Shuten was lying before, saying they didn't harm either of them. She asks them to defeat the Swordmasters and prevent the Onriedo's arrival. After she disappears, Kotarou arrives with Onui and Tasuke. As the group leave the mountain, Kotarou realizes this world's divergence from the original history didn't begin in Shimosa nor Toke, as Danzo is still operational. Meanwhile at Katori Shrine, the Sorcerer orders Caster and Saber, the only ones who retained their sanity, to finish the ritual for the Onriedo.
Outside Toke Castle town, the Sorcerer prepares to materialize the Onriedo. On his order, Caster plunges the world into darkness, and replaces the sun with a blood red moon. The Sorcerer then uses the souls of five Swordmasters and their victims to transform Toke Castle into Onriedo Castle. Townsfolk are randomly turned into monsters and kill those who weren't turned due to Caster's Noble Phantasm. For those who lack resistance to magic have their human norms turned to bestial urges, and begin eating other humans. Among those killed is Sakon, who was killed by a child turned monster. The Sorcerer is revealed to be Amakusa Shirou Tokisada. He is not the Heroic Spirit Amakusa Shirou recorded in Chaldea, but a human who survived the Shimabara Rebellion in a now culled parallel world. As he traveled across many worlds, his grudge towards the Tokugawa grew until he became the living emodiment of hate, something beyond human. He then followed the calling of something that reach out to him, and arrived in this particular version of Shimosa.
Meanwhile at the hermitage, the group see the blood moon. They assume another Swordmaster has arrived. Danzo sends up a flying observational device to see that Toke Castle has been transformed. With Muramasa and the children, the group ride to town on the horses Muramasa provided.
Arriving in town, Kotarou scouts on ahead, and assumes the castle is the cause of the monsters in town. He also says a number of the townsfolk were turned into monsters. Danzo confirms the eastern area has been completely wiped out. Since the east is closer to the castle, the group assume people turn monsters when they get close to it. They then notice Otama helping people evacuate. After the ensuing monsters are slain, Otama confirms most of the survivors have already escaped an hour from when the carnage began. Yagyu and his samurai fought the monsters long enough for the survivors to escape. Otama also saw Kiyohime's servants fleeing from the castle, seeking refuge at the Town's outskirts. Muramasa then leaves the children in her care, as it would be too dangerous to take them to the castle. After they leave, two Orochi arrive. The group slay one, and encounter the Missonary who was fighting the other. He reveals Amakusa Shirou is preparing to use Onriedo Castle for a ritual, and Kiyohime is being held captive there. Amakusa Shirou plans to cast a far-ranging multilayered curse on the Tokugawa regime, one so powerful it'll threaten the stability of many parallel worlds. As his aim is to curse every possibility of Tokugawa regime, Amakusa Shirou plans to use Kiyohime as the perfect catalyst due to her Tokugawa heritage. Though she lacks blood from the immediate family, it will serve sufficiently for his plan, especially given that Iemitsu is only the third shogun. The Missionary realizes Amakusa Shirou was searching for a parallel world where Matsudaira's daughter was living near Edo following the Shimabara Rebellion. Once Kiyohime is sacrificed to the castle, it will be complete, and this world, along with many others, will be destroyed. The group then rush towards the castle to save Kiyohime and stop Amakusa Shirou.
The group arrive at the castle, and Danzo guides them to the courtyard. There she tries to confess she is an enemy spy, but Musashi reveals it before she can. The group suspected her at different times; Musashi and Muramasa from the beginning; Kotarou after Chiyome's demise; Ritsuka after Onui and Tasuke were abducted. Danzo reveals Saber commanded her to aid the group against the Swordmasters. Caster ordered her to kill them if the chance presented itself. Danzo believes she gained a soul, and guided the others to the castle of her own volition to stop its activation. Caster appears and mocks her for thinking such. He reveals he repaired her after finding her broken and abandoned body, having shutdown from a lack of magical energy. While he repaired her body though, he also altered her mental records. Musashi attacks him, but a barrier stops her. Danzo also tries to attack her from behind, but Kotarou stops her. Danzo realizes Caster has been controlling her actions the whole time. Caster then calls the monsters that he's been keeping at bay, which is why the group never encountered any in the castle so far. He also has Danzo fight the group, revealing he imbued her with a sorcery that recreates the Curse of Annihiliaton's karma through machinery. The group slay the monsters, but Danzo is too fast for them. Danzo then self-destructs herself. The explosion takes out Musashi's eye while leaving Danzo in critical condition. Ritsuka stops the bleeding with their Mystic Code, but Caster's curse imbued in Danzo prevents the eye from healing. Musashi attacks Caster with a slash that should have cleanly beheaded him, but he stops it. He then summons more monsters. Kotarou is then imparted with Danzo's magical energy, the very same that the first Kotarou embedded into her. He then helps the others slay the innumerable monsters summoned by Caster. Caster claims he cannot be harmed as long as Onriedo Castle has Satan's protection. He then casts the Curse of Annihiliation on Musashi to transform her into a Swordmaster. Ritsuka however uses the Mystic Code Rain of Isis to remove the curse. Musashi uses this opportunity to slash through Caster's multilayered barrier. Caster brings them into the other plane, and summons the great spirit of the Souma clan to fight on his behalf. Musashi slays the spirit, and Kotarou wounds Caster. While Myoujingri Muramasa should be the only blade capable of harming him, Kotarou was able to thanks to Danzo passing her will onto him. Kotarou then seemingly finishes off Caster.
Meanwhile inside the castle, Amakusa Shirou declares Onriedo Castle will destroy Chaldea after it destroys Shimosa. He spent twenty years travelling across different worlds before Satan called to him. He saw the Tokugawa have repeated the massacre of Christians at Shimabara across several worlds. Thus, he will kill every Tokugawa mercilessly despite knowing this world is cut off from the proper history. He then tells the guard that Musashi is in the castle. He declares he will kill her, believing it is the sole reason for his existence. She has yet to reach the pinnacle of her swordsmanship, while the guard already reached his. The guard is concerned he may not get the chance to duel her since she will be facing Saber first.
Mash, Leonardo da Vinci, and Sherlock Holmes make contact with Ritsuka. Da Vinci reveals something intervened with Ritsuka's dream and brought their consciousness somewhere else. Since Chaldea already had data of a similar situation, they were able to surmise what happened, but they couldn't reach Ritsuka. The only thing that eventually worked was rayshifting Kotarou thanks to his strong connection to the still living Danzo. Kotarou realizes the spell meant to restore Ritsuka's comms he brought with him was activated when he absorbed Danzo's magical energy. However they will not last long since that world is outside the proper history. Sherlock explains Ritsuka's mind was able to attain something similar to a physical body after being transported. Even though the body is only temporarily, if it didn't adjust to this world, Ritsuka's magic circuits wouldn't function properly to restore their comms. Ritsuka realizes Shuten restored their circuits when she punctured them, suspecting she shared memories with herself in Chaldea. Sherlock then reveals Ritsuka was brought into the rift between reality and dreams. Shimosa isn't a Singularity, instead it is akin to a Reality Marble; an alternate world that poses no threat to humanity. Musashi is a Mobile Singularity, but she isn't the only factor responsible for what happened to Ritsuka. When multiple Mobile Singularities are in the same world, a number of abnormalities and unusual phenomena will occur. Ritsuka and Muramasa deduce Amakusa Shirou is the other Mobile Singularity. Kotarou realizes monsters manifested in Shimosa when Amakusa Shirou and the Swordmasters arrived, with more appearing when Onriedo Castle manifested. Sherlock originally hypothesized that Musashi would be able to control the monsters like Amakusa Shirou can. She couldn't though, so he suspects Amakusa Shirou has a stronger Mobile Singularity temperament than her. After communications end, the group enter the castle keep.
The group reach the keep's 4th floor when Caste tries to ambush Musashi. However before either can do anything, Saber kills Caster. Saber then reveals himself to be Yagyu, the only human among the Swordmasters. He reveals he joined Amakusa Shirou for a chance to duel Musashi again. Ritsuka and Musashi stay to fight Yagyu, while Muramasa and Kotarou ascend to the 5th floor. Yagyu brings Ritsuka and Musashi to the other plane for their duel. Eventually Musashi awakens her ultimate techinque, Kengou-Battou: Ishana-Daitenshou, to breakthrough Yagyu's god-like swordsmanship. Yagyu then dies thanking her for the duel.
On the fifth floor, Amakusa Shirou prepares to sacrifice Kiyohime when Muramasas and Kotarou arrive. Muramasa realizes the Counter Force summoned him to stop Amakusa Shirou, who became a threat to the world. Amakusa Shirou's body is now equal to a Swordmaster, so Kotarou and Muramasa's attacks are useless. Ritsuka and Musashi then arrive to help fight him. He eventually entraps them inside his Reality Marble, Shimabara Hell. It is recreation of Amakusa Shirou's original world engraved into his soul, where the very air is poisonous. It doesn't suffer any living person to survive, and there is no escape from its waves of suffering and resentment. Muramasa forges Tsumugari Muramasa, and bisects both the Reality Marble and Onriedo Castle. As the castle burns around them, Muramasa explains his sword could reach outside the Reality Marble because Onriedo Castle shares part of its name with Edo Castle. The name Muramasa is synomous with the Tokugawa's downfall, so Amakusa Shirou would have succeeded if he didn't rhyme the name of his castle with the Tokugawa's own. Kotarou then pierces Amakusa Shirou's heart with the kunai that Chiyome left behind, and finishes him off. Deducing Ritsuka and Musashi are on the otherside of the keep, Muramusa has Kotarou to escape with Kiyohime. He then disappears since he used a divine sword without the body of a god.
Meanwhile, Ritsuka and Musashi try to escape from the burning castle when Amakusa Shirou's guard, Sasaki Kojirou, confronts them to kill Musashi. Despite having never met him, Musashi knows his name, and senses he is her fated rival. It doesn't when and where, Musashi and Sasaki are destined to fight. Though the duel itself is void of meaning or purpose, it doesn't matter to them. As their duel continues, their sword techniques are evenly matched while surpassing time, space, existence, and essence. Musashi's zero is a skill that arrives at a single correct answer amongs many possibilities. Sasaski's infinity is a skill that creates and accepts many possibilities. They eventually reach the Realm of Infinity, or the Realm of Nothingness. There is no time, no space, no fate, no good, and no evil within this realm. It is devoid of thought or feeling; a place only true masters of the sword can reach. It is not a world; it is neither the proper history nor culled history; it is beyond even the rift of reality and dreams. It is an impossible domain where zero and infinity clash endlessly. Musashi and Sasaki would duel each forever if not for Ritsuka determining Musashi as the winner. Satisfied by their duel, Sasaki escapes from the castle. Though she is the victor, Musashi recognizes she is too weak now to escape. She then throws Ritsuka out of the keep to show her thanks for them staying by her throughout her journey. They're caught just in time by Kotarou. Musashi dies amidst the flames, satisfied she reached the Void.
At Toke Castle town, Kiyohime thanks Ritsuka for saving everyone. She says the castle will be rebuilt after the town is taken care of. After Otama asks them where Musashi and Muramasa are, Ritsuka goes to their room in her inn. They ask Kotarou if Murasama's Spirit Origin will be registered in Chaldea. Kotarou doubts it since this Shimosa exists in the rift between reality and dreams. Nothing that happens in this Shimosa can ever affect the proper history. Ritsuka realizes they can never return this particular Shimosa ever again. Later, they dig through the wreckage of Toke Castle and finds the tsuba Musashi used as an eyepatch.
Meanwhile, Caster is revealed to be still be alive. He is frustrated his plan to destroy Shimosa was thwarted. His True Name is then revealed to Ashiya Douman. While he failed to invade Chaldea, Douman was able to find information on the lost history (Missing Belt). This Shimosa is similiar to a parallel world without being one; it is part of human history without being part of it; It is a world observed by the god of a distant star; a world resembling a Singularity yet isn't. Douman reveals Satan was a temporary name for his master as a joke. Their name isn't revealed though, for it is a great curse upon the world.
Ritsuka recovers from their coma. Kotarou arrived first and gave the full details about what happened. Da Vinci says Chaldea's library doesn't have any records of what occured, so she will make it herself. They'll also need to find the true identity of Satan. Da Vinci tells Ritsuka she'll debrief them later on their experience. On their way to their room, they encounter Edmond. He denies being the Missionary they met in Shimosa. He then tells them to check their desk before sleeping. There they find a prerecorded video message from Musashi. Edmond told her to record it before she continues her journey. Musashi reveals she died, but she later woke up. From there she crossed many worlds until she arrived outside of Chaldea, where she encountered Edmond. Sherlock told her she is a now Heroic Spirit who materialized outside Chaldea thanks to a Chaldea summoning spell. Thanks to her connection with Ritsuka, her Spirit Origin was recorded as a Heroic Spirit after she died. She is now a Servant who automatically forged a contract with Ritsuka as her Master. Sherlock found it strange though that a "what if" Heroic Spirit who shouldn't exist could be summoned. Musashi ends the recording hoping to see Ritsuka again someday, addressing them as Master.
|Saber (Living Hero)||Miyamoto Musashi||Ritsuka Fujimaru|
|Saber||Sengo Muramasa||Counter Force|
|Lancer of Purgatorio||Inshun Hozoin||Heroic Spirit Swordmasters|
|Assassin||Fuma Kotaro||Ritsuka Fujimaru|
|Archer of Inferno||Tomoe Gozen||Heroic Spirit Swordmasters|
|Saber of Empireo (Living Hero)||Yagyu Munenori||Heroic Spirit Swordmasters|
|Assassin of Paraiso||Mochizuki Chiyome||Heroic Spirit Swordmasters|
|Caster of Limbo||Ashiya Dōman||Heroic Spirit Swordmasters|
|Assassin (Living Hero)||Katō Danzō||Heroic Spirit Swordmasters|
|Rider of Kālasūtra Hell||Minamoto no Yorimitsu||Heroic Spirit Swordmasters|
|Berserker of Saṃghāta Hell||Shuten-dōji||Heroic Spirit Swordmasters|
|Avenger (Living Hero)||Amakusa Shirō Tokisada||Heroic Spirit Swordmasters|
|Nameless Saber||Sasaki Kojirō||Amakusa Shirou Tokisada|
|Human||Onui and Tasuke||Sengo Muramasa|
- ↑ 1.0 1.1 1.2 About Shimousa, Information translations by Fallacies
- ↑ 2.0 2.1 2.2 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 13: The Stage of Carnage, Onriedo (Beginning)
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 15: The Stage of Carnage, Onriedo (Ending)
- ↑ 4.0 4.1 4.2 4.3 4.4 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 14: The Stage of Carnage, Onriedo (Middle)
- ↑ 5.0 5.1 5.2 5.3 5.4 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 16: See You Again Something, Flower at the Apex of Heaven
- ↑ 6.0 6.1 6.2 6.3 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 2: Purgatorio (Middle)
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 5: Inferno (Middle)
- ↑ 8.0 8.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 4: Inferno (Beginning)
- ↑ 9.0 9.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Prologue
- ↑ 10.0 10.1 10.2 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 1: Purgatorio (Opening)
- ↑ 11.0 11.1 11.2 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 3: Purgatorio (Ending)
- ↑ 12.0 12.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 6: Inferno (Ending)
- ↑ 13.0 13.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 7: Paraiso (Beginning)
- ↑ 14.0 14.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 8: Paraiso (Middle)
- ↑ 15.0 15.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 9: Paraiso (Ending)
- ↑ 16.0 16.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 10: Kalasutra Hell (Beginning)
- ↑ Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 11: Kalasutra Hell (Middle)
- ↑ 18.0 18.1 Fate/Grand Order - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Section 12: Kalasutra Hell (Ending)