Patchwork London Singularity

Lady Reines Case Files refers to an event, part of a collaboration between Fate/Grand Order and Lord El-Melloi II Case Files.

Setting
When the survivors of Chaldea established their new base at the Wandering Sea, an old subsystem created by Leonardo da Vinci was suddenly reawakened when transferring data from the Shadow Border. The subsystem was designed to verify the existence of the Master after Rayshifting, in case of an emergency where staff members were dead. It was called Mnemosyne, but due to technical issues, it was never implemented. Upon reawakening, Mnemosyne discovered that A-Team betrayed humanity, the Fantasy Trees turned the world blank, and Da Vinci had died. It then decided to use its powers of observation in conjunction with the Holy Grail it attained to create a Singularity at the end of 19th century London. The structure of the Singularity consisted areas, each of which are vastly different from each other centered around a theme, called Patchworks. Ritsuka and El-Melloi II soon rayshifted to the Singularity, but they were separated and lost contact with Chaldea.

By the time Ritsuka awakened in the Singularity, it was already on the brink of collapse, so Mnemosyne consumed their memories to extend the Singularity's life. It was at this point that Mnemosyne decided it can determine what is true, and use its powers to make Ritsuka forget their sorrows. However, since fabricating new memories would prove difficult, Mnemosyne sought to have Ritsuka find the paper scraps containing their memories in order to make it easier for them to accept the fabricated ones. These scraps were then placed in the Singularity's three Patchworks where they proceeded to take residence in what is closest. Due to the scraps though the residents of these Patchworks lost some of their memories in following certain motives behind them. At some point, Mnemosyne created a copy of Rhongomyniad from Ritsuka's memory of it to serve as its body, and disguised it as the Clock Tower. It also planned to use the energy extracted from everyone's memories, enhanced by the Singularity's vast mana, to fabricate Ritsuka's memories.

El-Melloi II sensed something was amiss with the Singularity, and proceeded to investigate the matter. Eventually though his investigation drew the attention of Mnemosyne, forcing him to separate Zhuge Liang's Spirit Core from his body to create a dead copy of himself. While the action left him with nearly none of Zhuge Liang's powers, it enabled him to continue investigating without being detected as a Servant. He also activated Chu Shi Biao, which caused Reines El-Melloi Archisorte and Luviagelita Edelfelt to be summoned into the Singularity as Pseudo-Servants fused with Sima Yi and Astraea along with Gray, who was summoned as a regular Servant. Astraea searched for the paper scraps on her own to stop Mnemosyne's plan, hiring EMIYA to help her. Gray went out to search for El-Melloi II to discover what happened to him. Unfortunately, Reines was summoned without her original memories, and believed herself to be El-Melloi II.

History
Ritsuka is woken up on a train by a mysterious girl, who addresses them as her disciple. She introduces herself Lord El-Melloi II, and asks if they remember now. Ritsuka sees vague memories of Sherlock Holmes, Goldolf Musik, Mash Kyrielight discussing their latest rayshift, but they can't remember who they are. Carrying El-Melloi II's luggage for her, the pair exit the train to London. El-Melloi II suggests first returning to the flat when Ritsuka asks about the black tower in the distance. She answers that it is the Clock Tower, the headquarters of the Mage's Association. Eventually the pair arrive outside of her flat, but she notices its Bounded Field has expanded and now blocking voices. She then forces an automaton that ambushed them. Feeling like they're being watched, she and Ritsuka enter her flat.

The pair find the corpse of the real El-Melloi II in the study. The false El-Melloi II becomes confused as to why she thought she was El-Melloi II. She notices an "M" written in blood near El-Melloi II when an automaton suddenly bursts in. After defeating the initial automaton, reinforcements arrive, so the false El-Melloi II orders an immediate retreat by jumping through the window. Despite them being on the fourth floor, she pushes Ritsuka out of the window. She then follows after activating Trimmau.

Upon landing outside, the false El-Melloi II throws magical bombs to destroy the automatons inside before retreating with Ritsuka and Trimmau. She then introduces herself as Reines El-Melloi Archisorte, younger sister of El-Melloi II. She questions why she assumed she was El-Melloi, and why he was murdered. Trimmau also thought Reines was El-Melloi II until a moment ago. She then introduces herself to Ritsuka; Reines explains she is her maid that originally belonged to Kayneth El-Melloi Archibald as the Mystic Code, Volumen Hydrargyrum. She ponders if a simple suggestion spell made her believe she was El-Melloi II, though it shouldn't have affected Trimammu then. She asks Ritsuka if they remember anything, and if they know about her. However, they only know her name. Reines surmises they both have amnesia and falsified memories. She then realizes the town is closer to the 19th century when it begins to warp. As it warps, a garbled transmission comes from Mash, saying something about spirit graph trunk. After the transmission cuts, the town is warped into a bizarre scenery. Reines realizes the trunk Ritsuka is holding isn't her's. She surmises it is the spirit graph trunk invented by Leonarod da Vinci to summon on the go. She then decides they need to find the one who killed El-Melloi II and stole their memories. Though she is stumped on how to proceed with their investigation, she knows El-Melloi's dying message is their leading clue. She wonders about the bizzare scenery when a giant reveals the town is called Patchwork London, a patchwork of fairy tales. After the giant introduces herself as Paul Bunyan, Reines asks her if she knows anything about the "M". Bunyan says she does, and lets Reines and Ritsuke ride on her shoulders.

Bunyan takes the pair to a museum, where she is welcomed back by Sakata Kintoki and Jack the Ripper. Ritsuka suddenly recalls meeting them before. Bunyan wonders if Ritsuka and Reines could help find her friend. However, neither she nor Kintoki can remember who it is when Reines asks. Bunyan explains the museum is filled with enemies that Kintoki and Jack couldn't defeat themselves. Since she cannot go in herself, she sought help when she found Ritsuka and Reines. Reines agrees to help, and ask Bunyan about the enemy's identities. Just as Bunyan begins to describe them, a horde of monsters appear that Jack identifies as the ones from the museum. In response, Ritsuka uses the trunk to summon Servants to help fight the monsters. Afterwards, the group enter the museum.

As the group explore the museum, Kintoki explains that he, Jack, and Bunyan are Stray Servants. However, neither he nor Jack know for what purpose they were summoned. Reines deduces a mage was responsible for El-Melloi II's death since they'd have more motive than a normal human in the pursuit of magic. She also suggests a villainous Servant may be the culprit. After exploring the museum, the group are ambushed by monsters. They then leave the museum after killing the monsters.

Outside of the museum, Reines states she assumed nobody would be inside, and asks Jack when her friend went missing. But neither Jack nor Kintoki can remember, which makes Reines find the whole incident even more bizzare. She then suggests allowing her and Ritsuka to explore the museum on their own. After Kintoki allows it, the pair go back into museum.

Inside the museum, Trimmau uses her liquid form to inspect the entire building but finds no hidden rooms. Ritsuka then suggests searching the library. There the pair find a talking book hidden amongst the others. Reines deduces it is Bunyan, Kintoki, and Jack's missing friend, and that their true form is of a book. Ritsuka then gets a sudden flashback of meeting them before. After the book takes the form of a young girl, Reines deduces she forget she could do that. She further deduces the girl forgot about her friends when she was hidden away, yet she doesn't know when everyone forgot. She then suggests the girl being hidden away and the Servants losing their memories happened simultaneously. The girl then introduces herself as Nursery Rhyme, and says she can't remember anything past searching with Bunyan, Kintoki, and Jack. Reines tells Nursery Rhyme that her friends are waiting at the museum's entrance. After Nursery Rhyme leaves, Reines notices a scrap of paper where Nursery Rhyme in her book form was. The paper reads Mnemosyne, which makes Reines wonder if it is what El-Melloi II's dying message referred to. She then suddenly remembers that she is a Pseudo-Servant. Ritsuka sees flashbacks from their time at Chaldea, and remembers they are Chaldea's and Mankind's final Master. They are then contacted by Mash, and tell her that El-Melloi II was murdered and they lost their memories. Mash then reveals Ritsuka rayshifted into a Singularity that appeared at the end of 19th century London. She also reveals El-Melloi II was the Servant selected to accompany them. During the rayshift though, communications were completely severed, and Ritsuka and El-Melloi II's signal was lost. Chaldea needed to reset communications and other systems just to barely allow Mash to contact Ritsuka. Ritsuka and Reines then leave the museum to find the cause of the Singularity.

The pair arrive in a new territory of Patchwork London that differs from the bizarre scenery of the previous territory. They notice everyone is wearing masks, so Reines decides to call the territory Patchwork Masquerade. She deduces each Patchwork is centered around a theme, with first Patchwork being fairy tales. Mash asks the pair if they've noticed anything strange in their memories. Reins replies it would be difficult to tell currently, but they'll be cautious nonetheless. Mash agrees to tell them immediately if she notices anything. She then detects al large source of magical energy nearby. Reines deduces it's from the palace, the. After Mash cuts transmission, the pair enter the palace.

Upon entering the palace, Reines deduces it is a patchwork of its history. The Masquerade soon begins; Reines questions why the pianist is absent despite the piano being the central performance. The music causes Ritsuka to remember Antonio Salieri, but they're able to answer Reines if it's him playing the music now. The piano then stops in the middle of the song, which has apparently happened before. A citizen says the piano has recently stopped played as soon as it begins. The pair decide to take on this particular case when an old man arrives and tells them to wear masks. He then hands them masks that they proceed to wear. He introduces himself as M since the Masquerade is where names aren't given. Ritsuka reacts under the assumption of M that refers to El-Melloi II's dying message. Reines quietly warbs them not to react so openly, and they need to think on how to proceed if M is the murderer or an accomplice. She then asks M who it was playing the music before, but he answers that nobody knows. He explains the pianists' identity is unknown since every investigation involving them is unauthorized, and the only know fact about them is they reside in the palace. He then decides to take the pair to the Bloody Tower where the pianist is supposed to be.

Outside the palace, M warns the pair that the Bloody Tower's security is strict on this particular path. He tells them to scale up the wall while he distracts the guard. He proceeds to start distracting the guards when mask wearing ghosts suddenly appear. After destroying some ghosts, the group enter the tower.

Inside the tower, Reines asks M to go on ahead while she speculates on the ghosts, After he leaves, she says they still don't understand the intricacies for recovering their memories. She compares them forgetting their memories to drinking from the, river of forgetfulness. She contrasts this to drinking from the waters of Mnemosyne, Lethe's counterpart which grants knowledge. Ritsuka recalls the name being written on the paper scrap they found in the museum library, to which Reines she explains it is the name of the goddess of memory. She then suddenly asks herself regarding a particular question. She explains that was Sima Yi, the Heroic Spirit that possessed, though the fusion appears to be inefficient. She then states Sima Yi's question was to ask why he was summoned, which she also wants to know. The pair then hear a shriek and proceed to go where it came from. They arrive in a room where they see a man being overwhelmed by mask wearing automatons, along with M. After the automatons are destroyed, Reines notices the pianists is gone, and assumes the automatons kidnapped him. The man introduces himself as William Shakespeare, who Ritsuka suddenly remembers meeting in the London Singularity. He explains he wanted to see the pianist himself, and reveals M lied about names being banned in the Masquarede. The Queen and a number of guards then enter the room, and demands to know why M came to the tower. She assumes the pianist being missing is his doing despite him being the one who introduced her to the pianist. M responds that he and the others came to the missing pianist as well. Reines decide to find the missing pianist with Ritsuka, and the Queen agrees to reward them once the case is resolved. After the Queen and her guards take M and Shakespeare away, Reines says all three of them are connected to the pianist. She however says it's not time to discuss that now, and fires a blast at a figure behind the piano. Assassin asks how she knew, to which Trimmau answers Reines noticed the mana in the area was strange. He says he isn't the kidnapper, and proceed to flee out the window, with the others giving chase.

Landing outside the tower, Reines orders Trimmau to not let Assassin escape. While they're fighting, Reines decides she and Ritsuka should help Trimmau after seeing Asssassin's high-speed and concealed movement. Assassin tries to shoot her, but Trimmau protects her at the cost of damaging herself. In response, Reines activates Sima Yi's Noble Phantasm, Unspeakable Formation, to restrict Assassin's movement. The pair fight him as he struggles, but he stops when his client arrives. She calls him Kerry, and Reines recognizes her as Luviagelita Edelfelt and she is a Pseudo-Servant. Luvia demands the paper scrap they found in the Patchwork Fairy tale, claiming it's for their own good. Trimmau tells Reines it's impossible to read Luvia's mana statistics at present, and Reines realizes Luvia is fused with a Divine Spirit. After Luvia and Kerry leave, the pair are contacted by Mash. After Reines tells her about the missing pianist, Mash says it's possible they are connected to paper scrap Ritsuka and Reines found earlier. Reines decides they should chase after Luvia and Kerry since they have no other leads. But since Luvia is a Divine Spirit, she decides to question the suspects in the case of the missing pianist. After questioning the suspects, Reines orders Trimmau to sift through her unconsciousness for anything keywords that are important. She then asks Sima Yi what they should be looking for, and he answers they look for the mysteries they do not yet understand. Trimmau reports she has discovered three keywords: memory loss, ghost, and Pseudo-Servant. Reines ponders about the connection when she realizes something about the pianist, and tells Ritsuka to follow back to the piano room.

Upon returning to the piano room, Reines finds a Mnemosyne scrap like she deduced they would be. She explains Luvia talked about it earlier, and she was able to understand since their logic as Pseudo-Servants earlier. She continues the automatons had specific human memories instilled into them, which allowed them to move. She deduces it was Mnemosyne scraps' magic that made it possible; everyone, including the Queen, knew, but they forgot. She then invites M into the conversation, sensing he was eavesdropping. M remembers Salieri wasn't able to become a Servant in the Singularity because his Saint Graph wasn't sufficient enough. So he and Shakespeare used the ghosts wandering throughout the Tower of London as a substitute for Salieri. M created the plan, Shakespeare did the composition, and they used the Mnemosyne scrap they found coincidentally for mana. They then presented the fabricated Salieri to the Queen, and she accepted their arrangement. M questions why and how they could have forgotten. Reines explains they had forgotten the pianist was a facade, which eventually caused the automatons to attack. She asks M where the automatons came from, but he answers they were there beforehand. He then confesses he merely wanted to make people dance with the melodies of the ghosts played through the piano. Reines prepares to retrieve the Mnemosyne scrap when she notices Luvia. Ritsuka and Reines then fight her while M holds Kerry off. The pair are struggling aginst Luvia when Automatons arrive to capture Reines, who they assume to be El-Mello II. They quickly destroyed though by Gray, and Ritsuka restores the Mnemosyne scrap.

After re-experiencing their battle against Goddess Rhongomyniad, Ritsuka is woken up by Reines in a strange mechanical room. She explains M fled, and they are in a hotel she rented in the third Patchwork: the Patchwork of Dazzling Steam. She then introduces Gray as El-Melloi II's disciple when Mash asks about her. She asks her if she knows they're still in London, and Gray replies she knew because of her presence as a Servant. However she isn't sure why she was summoned similar to Reines. After Ritsuka forms a temporary contract from Gray, Reines reveals the Divine Spirit possessing Luvia is Astraea. She then says Gray's Noble Phantasm should be able to breakthrough Astraea's defenses. Add then introduces himself, and explains he can change into a weapon for Gray. Mash reveals through her analysis of the two previously collected Mnemosyne scraps that there are smaller scraps in Patchwork London. The group set out to find and restore the scraps.

Outside of the hotel, the group see a parade of automatons along with steam-powered horse riders. Reines notices a horse and carriage in the center of the crowd, which contains the Patchwork's king, Charles Babbage. Reines decides to visit him alone to ask for his help. She eventually returns with the Queen, who had looking for them to grant their promised reward. The Queen asks what they want for a reward, to which they answer they wish to meet Babbage. She agrees to take them to him since she was already planning to meet him herself.

The Queen takes the group to the throne room of Babbage's castle. Babbage then arrives and welcomes her, and she tells him how the other previously solved the case of the missing pianist. After learning of their search for the Mnemosyne scrap, Babbage asks them to destroy his kingdom since it is an unnatural realization of his dream. He says he reached this conclusion thanks to the guidance of Astraea, who appears in the room. She reveals all of the people of Patchwork London, including herself, are missing memories. She ascertain it was necessary to compensate with the scraps, so she went searching for them in the Patchwork Masquerade after meeting with Babbage. Reines asks Babbage where the scrap is, and he replies it is infused into his body. He explains the scraps are central part of each Patchwork, and immediately seek residence in what's closest. He requests the group kill him since the scrap is likely infused into Spirit Core, but calls it a last resort when they refuse. He reveals Astraea searched for an alternative in the other Patchworks, which explains why Ritsuka and Reines met her in the Tower of London. He tells the group to locate his subsystem located somewhere in his castle.

Later, as the group search the subsystem, Gray finds a particular spot on a wall. Ritsuka then opens it to reveal a secret passage. The passage continues on underground, and eventually the group encounter steam ghosts that Reines calls unnatural. After the ghosts are destroyed, Reines explains it is essentially Gray's job to track and fight spirits. She calls the steam ghosts bizzare, which Add concurs with when he says they tasted like haze. She then asks Ritsuka what ghost are, and they answers they are dead people. Gray explains however that ghosts are actually created memories of the deceased's actions when they alive. Reines explains ghost act on the memories from their past, but the steam ghosts aren't acting on that. The group then soon reach the core of the castle, a massive steam engine. They witness ghosts being extracted into it, and they deduced the ghosts' magical energy is being used to power the engine. Reines then realizes it isn't a steam engine, and Trimmau reports the engine has traces of Mnemosyne scraps that someone retrieved prior. Reines surmises the steam ghosts are the results of the mana from the scraps and ghosts fusing with the steam. After destroying the steam ghosts that appeared, the group find Babbage's subsystem, the. Reines uses it to discover that it was El-Melloi II who retrieved the scraps. She ponders why the scraps were in the engine in the first place when she realizes Babbage forget. She further realizes the enemy's goal wasn't to consume their memories, instead to use the energy from those memories. She also explains the energy retrieved the ghosts' memories isn't particularly large. Gray says the mana from the ghosts in the castle and Tower of London all had irregular mana thanks to the Mnemosyne scrap. Reines calls they're coming to the Singularity, and the efficiencies of using memories for energy to be irregular. She then realizes the Difference Engine has been working independently, and it is the source of the automatons in Babbage's patchworks. She then says they need to return to El-Melloi II's flat immediately.

The group return to Patch Fairy Tales, and discover its terrain has been warped into a city consumed by fire. Automatons and steam ghosts then emerge from where El-Melloi II's flat was in large numbers, piling up like a mountain. Mash confirms the scrap is nearby, and Reines deduces El-Mello II kept it for safekeeping. She further deduces Astraea and Kerry used the Difference Engine to reach the same conclusion, as they both arrive. Astraea reveals the Mnemosyne scraps are utilizing scraps of a Holy Grail, whose mana eventually form the Patchworks. She then uses her Noble Phantasm, Custos Morum, to destroy the mountain of automatons and steam ghosts, then proceeds to retrieve the final scrap. The group then give chase to reach the scrap before she does while fighting through enemies, and avoiding the remaining stars from her Noble Phantasm. However, far too many enemies stand in their way, as Astraea nearly reaches to the scraps. Gray prepares to unleash her Noble Phantasm to stop her when Kerry arrives and stops Gray. After Kerry is defeated, Gray prepares again to unleash her Noble phantasm as Add consumes mana from the automatons and steam ghosts. Astraea unleashes Custos Morun to block it, but Gray's Rhongomyniad is easily breakthroughs. With Astraea down, the group rush to reach the scrap. However upon touching the scrap, Ritsuka finds their memories of da Vinci are being erased. A figure tells them to accept those as no longer being the truth when someone breaks the process. The individual is revealed to be El-Melloi II, who reveals the scrap was a trap. Reines and Mash doubt it's really him though, so he asks why would a Servant leave behind a corpse. He explains that as Pseudo-Servant, he has two Spirit Cores: his and Zhuge Liang's. He created a corpse of himself through separation of use of Zhuge Liang's Spirit Core. The downside to this action though was that he lost almost all of Zhuge Liang's powers. The upside to it though it is that with Zhuge Liang's powers close to nil, it allowed him to investigate without being detected as a Servant. He then reveals the Singularity's vast mana increased the normally inefficient energy drawn from their memories. He explains using the scraps caused the Singularity's vast mana to encroach on their memories and fabricated them, which is the enemy's goal. He suspects Ritsuka's memories were stole from them from the moment they arrived in the Singularity. However, even with their memories stolen though, fabricating memories would be prove difficult since their memories of a particular Servant would resurface if they reencountered them. Thus in the order to rewrite memories, the enemy arranged the scraps to placed at a certain locations for Ritsuka to retrieve. El-Melloi II explains the first and second scraps contained Ritsuka's original memories while the third one was meant to implant the fabricated memories. He concurs with Gray that Chaldea would know whether Ritsuka's memories are true or not. He asks though why they've been only receive transmissions from Mash, and explains the enemy needed someone Ritsuka absolutely trusted to guide them. Reines the deduces the M in El-Melloi II was for Mash. He reveals the Mash the group has been talking to thus far is a fake. After the fake Mash blocks communications, El-Melloi II explains the enemy fabricated the fake Chaldea and Mash in order to get the group to believe in their information reports in order to guide them. He deduces the enemy's goal isn't to destroy them, but rather something to do with the scraps. He cannot deduce anymore though with his analysis of the final scrap, but he says Babbage could help provide a deeper analysis. The group then return to Babbage's castle with El-Melloi II, Astraea, and Kerry.

Babbage agrees to analyze the scrap, believing it may provide clues that link to the enemy. He then invites the group to rest in his castle since the analysis will take time. Astraea asks him why Ritsuka needed false memories implanted into them. He replies that finding the enemy could provide the answer, and asks who was the particular person in Ritsuka's memories that were being erased. El-Melloi II deduces the enemy pities them, with good yet ill intentions. Reines then realizes the reason why she, Luvia, and Gray were summoned into the Singularity was because El-Melloi II failed. She explains he failed when he created the corpse because he was driven into a corner. She continues she, Gray, and Luvia were more inclined to be summoned to solve this particular case due to their deep connections with El-Melloi II. She then deduces they're summoning as Servants was due to Zhuge Liang's Noble Phantasm, Chu Shi Biao. El-Melloi II explains it grant allies the abilities they need, and in this case, providing Reines, Gray, and Luvia with Servant Saint Graphs. He states though its effects wouldn't be that tremendous unless the Singularity's circumstanced put a strain on humanity. Reines deduces Sima Yi was summoned thank to his connection with Zhuge Liang. Later, El-Melloi II reveals the Singularity was ready to collapse when Ritsuka woke up, and it consumed their memories to lengthen its lifetime. The group then rush to the castle's balcony when Reines rushes to retrieve them. Reines deduces their awareness of the Clock Tower was obstructed, so they never realized it was a fake Rhongomyniad. Babbage reports a large number of steam ghost and automatons are emerging from its interior, though they seem peaceful for now. He agrees with El-Melloi II's concerns though, and says there is an 80% chance of them invading his Patchwork to capture Ritsuka. He also says the enemy has been driven into a corner now that they've unveiled the fake Rhongomyniad. He then gives his analysis of the final scrap, revealing the enemy is related to Chaldea. El-Melloi II assumes them to be a traitor since they knew both Mash's appearance and mannerism. Babbage then gives the second name revealed in his analysis: Mnemosyne, a system of Chaldea. Reines and Astraea decide to assault the fake Rhongomyniad, but Babbage warns against it with all of the enemies swarming out. Gray says she could clear a path, but she doesn't have sufficient mana to do so. El-Melloi II suggests collecting the smaller scraps for mana, and asks Babbage to provide a countermeasure against their fabricated memories.

Joined by Babbage, the group search for the smaller scraps, and fight through their fabricated memories. A memory of fighting Ultra Heroine Z, except a alternate version of Mysterious Heroine XX called Super Heroine ZZ also joins in. A memory of the first battle against Gawain at Holy City Camelot's main gate during the Camelot Singularity, but his Gift of Nightlessness doesn't function. A memory of the battle against Black Iri, though she later transform into a corrupt version of Illyasviel von Einzbern. A fabricated memory of fighting Medea and Heracles during the Okeanos Singularity. A fabricated memory of fighting a horde of corrupt Musashibou Benkeis, who are weakened by Ushiwakamaru's Benkei - Steadfast Position and finished off by Jumping the Eight Ships at Dan-no-ura.

With the smaller scraps collected, Gray uses their mana to create a crystal staircase to the fake Rhongomyniad. While Ritsuka, Reines, Gray, and Astraea descend the stair, Babbage, El-Melloi II, and Kerry prepare for the onslaught of automatons and ghosts. Meanwhile in the Patchwork Fairy Tales, Bunyan, Jack, and Kintoki fight against the hordes of automatons and ghost. Simultaneously in the Patchwork Masquerade, the Queen and Shakespeare also fight against the automatons and ghost. Meanwhile as they continue ascending the stair, the group are transported into a fabrication of the Battle of the Time Temple by a sudden Mnemosyne scrap. There they are confronted by fabrications of Lev Lainur Flauros and Barbatos. Ritsuka recalls fighting Barbatos in the London Singularity, and Reines realize the enemy is using that link to create the fabrication. Astraea then proceeds to bombard Barbatos and the Demon Gods of the Control Room with Custos Morum. Reines uses her Noble Phantasm to extract Ritsuka's memories of fighting the Demon Gods as magic. After the group fights against Barbatos several times, Reines uses Unspeakable Formation to rewrite the fabrication into the true memory of when Ritsuka destroyed the Demon Gods. After destroying Barbatos, the group exit the fabricated memory, and continue ascending the stairs.

Eventually the group enter the fake Rhongomyniad's interior, but Astraea is suddenly forced outside. The enemy explains they created the fabricated memory from earlier in order to weaken Astraea since she was a major threat. Taking on the appearance of Da Vinci, the enemy reveal themselves to originally a program without form; Reines deduces she is Mnemosyne. Mnemosyne reveals she is a subsystem for verifying reality at the moment of rayshifting. She explains that prior to rayshifting, Staff members would verify reality at the destination to ensure the Master's safety. She was created as a system to ensure the Master still existed in the case of the staff being dead. However due to technical issues, Mnemosyne was never implemented. Reines asks her why she wants Ritsuka, but soon realizes she is trying to ensure they're protected. Mnemosyne demands they hand over Ritsuka, and proceeds to fight the group. The battle ends when they're struck by something akin to a Noble Phantasm, but Reines deduces Mnemosyne is using the memory of Rhongomyniad since the fake one is her body. She tells Gray to use Rhongomyniad, but Add says he's unable to do so. Mnemosyne reveals that just Gray can interfere with her Rhongomyniad, she can do the same to Gray's to prevent its activation. She also reveals she did so before they arrived since it would their key to a swift memory. She then proceed to use the Grail to transport Ritsuka into a space of memories.

In the space of memories, Ritsuka is shown Mnemosyne's oldest memory from when she was being still being constructed. However since she was never fully completed, she could only observe the Incineration of Humanity. After Humanity was restored, data was transferred into the Shadow Border, which caused her to change heavily. Mnemosyne reveals she recently reawakened when the Chaldea survivors established their base at the Wandering Sea; she wonders if it was due to heterogeneity of the Wandering Sea's data. However upon awakening, she discovered A-Team betrayed humanity, the world turned blank by the Fantasy Trees. Upon discovering her creator, Da Vinci, was dead, Mnenosyne decided she would use her functions of observation in the conjunction with her Grail to create the Singularity. She soon realized she could her observations to decide what is true. She also decided to use her power over memories to make Ritsuka forget all of their sorrows. She reveals she created the three Mnemosyne scraps to take their memories in order to guide to them. This was done to create new memories, and to make it easier for Ritsuka to accept them. Mnemosyne however didn't want to simply give them to Ritsuka, but having them go through proper tribulations to turn Ritsuka into their utmost version of themselves. That intention though was ruined by El-Melloi II's intervention, for which she apologizes. As Ritsuka becomes fatigued, Mnemosyne tells them to receive her memories, saying they will be free of things like sadness and torment. However, as she is erasing Ritsuka's memories, Gray uses Rhongomyniad to create a link into the space. Mnemosyne claims the effort is too later though, as she already has complete control over Ritsuka and their memories. Reines tells Ritsuka to remember the desperation they felt as they searched for the memories of those they forgot. She says that even if  they're happy without their memories, they will feel loneliness when they realize something is missing. Mnemosyne refutes that Chaldea has been too tragic for Ritsuka, claiming the reason she awakened was to save them from all of their sorrows and flaws. Ritsuka however refuses to let her take those away from them. Mnemosyne replies she will need to break them, believing they are lying to themselves to cope. She decides she will keep with her for many years until they are completely healed. However to her shock, something breaks through the exterior of the fake Rhongomyniad. It is revealed M used his Noble Phantasm at the cost of his life to increase its distance and damage output.

With Ritsuka out of Mnemosyne's space of memories, Astraea enters the fake Rhongomyniad's interior. She uses her second Noble Phantasm,Iam Redit et Virgo, to clear the sky of the smog that blocked Chaldea's communicators. Mash reveals they lost contact with Ritsuka after they rayshifted, but they still had their location. Ritsuka agrees with Da Vinci's request to stop her creaton. Reines then reveals the motives for each Patchwork. Patchwork Fairy Tale's motive was they wanted to be searched for; Patchwork Masquerade's motive was they wanted to talked without their identiies being known; Patchwork of Dazzling Steam's motive was wishing to forget. Reines then deduces Mnemosyne created the Singularity centered around memory loss because she was the one who wanted to saved. Trimmau reveals Mnemosyne and the fake Rhongomyniad is weakening due to Astraea's Noble Phantasm, so the group use this opportunity to finally defeat her. After being defeated, all of the memories that Mnemosyne had been collected begin to spill out from her. The fake Rhongomyniad then begin to collapse as well since it is her body. Before the group escapes though, Da Vinci tells Mnemosyne that she had no regrets regarding her death, and thanks her for grieving for her. Mnemosyne replies she was merely serving her function to observe. The group then escape the fake Rhongomyniad before it finally collapses.

With the fake Rhongomyniad now destroyed, everyone begins to disappear with the Singularity's imminent collapse. Astraea and Reines both wish the bonds they formed with Ritsuka will be summoned to Chaldea before disappearing. Meanwhile, Mnemosyne accepts she will lose the mana granted by the Grail and the Singularity will be resolved. She is glad she will no longer have to observe, and soon realizes she is now feeling true solitude. Da Vinci then appears to tell her that she did a great job, then she is finally shuts down.

Now back in Chaldea, El-Melloi II apologizes for getting Ritsuka into such a dangerous situation. He also deduces the Da Vinci that appeared before Mnemosyne at the end was due to Reines using Unspeakable Formation on her. It is then revealed El-Melloi II also accidentally brought Gray back with him. Gray reveals she has the Grail Mnemosyne used, and Da Vinci deduces it responded to the real Rhongomyniad and Gray's wish to stay with El-Melloi II. Gray apologizes, but Goldolf tells her the Grail is a physical record of her accomplishment. Ritsuka then welcomes her to Chaldea.

Participants
Servants

Non-Servants