Sigma (Σ) (シグマ, Shiguma?) is the "True" Master of Watcher in the False Holy Grail War of Fate/strange Fake. Despite having summoned Watcher, the shadows of Watcher claim that it is not meant to be a participant of the Holy Grail War, but rather a guide for Sigma himself to become the True Lancer (真ランサー, Shin Ransā?) Servant of the War "while living."
Sigma was raised by an unknown government to become part of a special forces unit that utilizes magecraft. He is the product of rape between Maiya Hisau and an unknown soldier possessing Magical Circuits to create soldiers for that unit. He wasn't given a name and was taken away from Maiya when he was a baby. He was among twenty-four children selected for the unit and given a Greek letter as code names, being forced to fire a gun when barely five years old, and enduring magical experiments. According to Francesca, as a result of the experiments he has a shorter lifespan than the normal person, but he will maintain his youthful appearance as someone in his late teens for a long time and will age rapidly when his time comes. The government, eventually collapsed with intervention from the Clock Tower to protect the secrecy of Thaumaturgy. Sigma became a mercenary, who served different people around the world, until coming under the service of Francesca and hired to become a participant of the Snowfield Holy Grail War. Francesca considers Sigma to be "her favorite pawn" that she would like to survive through the war.
Sigma treats himself as an ordinary soldier, calling himself simply Soldier A. He doesn't have any wish, desire, or anything to believe in, completely lacking faith in anything even being uncertain in his own abilities. He is rather cold, not feeling much about the death of his own mother in a similar Grail War that he is now participating. However, after summoning Watcher, Sigma starts seeing himself as more unique, making his own decisions that go against his superiors.
Sigma apparently has some knowledge of film-related details such as how he tries to hide Watcher's identity, informing others that Watcher is Charlie Chaplin, or how, when Watcher asked the young Magus if he knows about King Arthur's Holy Grail quest, Sigma responded that it's a Monty Python comedy which causes Watcher to fall silent.
Pre-WarEditFrancesca. He is told by her to become a Master, with Francesca not even giving him a catalyst, as she wants to see what the Grail itself picks. Although he is hired by Francesca, she tells Sigma to do what he wants, as it will make things more interesting. Francesca's associate, Faldeus Dioland though tells Sigma to keep in contact with him and inform him of what Servant he will summon. Sigma himself isn't interested in the Grail War, lacking a wish and only treating it as another task.
When Sigma finally summons his Servant, he is surprised to see that he has summoned numerous different beings. These beings, however, explain that they are simply shadows of the real Servant Sigma summoned, Watcher. Watcher doesn't show himself to Sigma, instead, watching over the Grail War, gathering information which the shadows then tell to Sigma. The shadows also tell Sigma that he is supposed to become the real True Lancer after he has completed several trials. Despite the unordinary circumstances, Sigma feels confident, not believing himself to be an ordinary soldier anymore.
As Sigma and the shadows continue talking the shadows eventually tell him that his first trial is about to begin, as False Assassin enters the house Sigma is in. Before Sigma even reacts, Assassin moves in front of him, questioning if he is a Master. Sigma manages to escape by distracting Assassin and jumping out of the window. As he tries escaping, he spots a girl, who he believes to be a bystander and telling her to run, endangering himself. However, the girl turns out to be a Master, named Ayaka Sajyou, who is the Master of Saber, who himself has formed an alliance with Assassin. Seeing Sigma endanger himself for a girl he doesn't even know, Saber decides to make an alliance with him, which Sigma accepts. Though allying with them, Sigma doesn't reveal the nature of his unique Servant, saying that he has summoned the Lancer Charlie Chaplin, who doesn't want to show himself.
While staying with Ayaka, Saber, and Assassin, Sigma also contacts Faldeus, also lying about his Servant, confusing Faldeus. After contacting him, Sigma talks with Assassin, who is still suspicious of him. Sigma tells Assassin that he lacks faith in anything, which is a contrast to Assassin, who is extremely religious. Assassin is though able to understand Sigma, realizing that he simply hasn't encountered anything worth believing in him. As she leaves him, she wishes that he will be able to find something to believe in. He stares at her, and the shadows tease him, asking if he has become smitten with her, which he denies.
Sigma later gets information from Faldeus of the house being surrounded which he tells to Ayaka and Saber. While they stay in the house, Sigma also informs them of the battle in the factory district between True Berserker and True Archer. Although Saber is intrigued by this battle, Sigma tells him that the battle will be stopped soon by his true employer, who is Francesca. This is true, as Francesca sent her Servant, True Caster to solve the issue.
Sigma also receives information from Watcher about Tsubaki Kuruoka, a young comatose girl who is also the Master of False Rider, who the police officers are trying to secure. Saber, Assassin, and Sigma decide to go help them, though when they arrive, True Archer and False Archer are also present.
False Archer becomes offended by Saber's presence and fires a volley of swords from Gate of Babylon at him. Saber easily knocks them away with his own sword, but Sigma is forced to run to avoid being hit with stray swords.
Sigma regroups with False Assassin, observing the battles. Watcher tells him that False Archer is Gilgamesh, and he tells this to False Assassin, claiming it is intelligence given to him by his superiors. When False Assassin says she will attempt to rescue Tsubaki, he questions the logic, pointing out that Tsubaki is a stranger so they should have no attachment to her, and saving her does not provide them with any tactical advantage in the war. She simply says there is no reason not to save a child. Sigma lets his resentment slightly show, pointing out no one saved him when he was a child. Watcher scolds him for his immature response. She then says that she wishes she could have met him as a child so she could have saved him.
After he tells her the room Tsubaki is held in, he offers to help, pointing out they may need two people to safely transport her. He then says after they rescue her, he'll tell True Archer that she is gone so that he'll hopefully not attack the hospital. Watcher asks him why he proposed that given he had earlier talked about not wanting to help because there is no benefit, and he is unable to answer.
They enter the hospital, where the staff have been made to fall asleep with Magecraft. False Assassin suddenly grabs him and yanks him to the side, saving him from being impaled by flying knives. Jester Karture emerges. Watcher quickly identifies him and tells Sigma his second trial has begun. Sigma notes that he's faced a Dead Apostle before, but he needed a lot of backup to beat it, and Jester seems much more powerful than that one. Jester explains that he is False Assassin's Master. If Sigma had chosen to abandon her, he would have killed him. At the same time, Jester cannot tolerate Sigma even spending time with her, and vows to make him suffer. Jester believes Sigma and False Assassin are an item, and wonders what look will be on her face once he is through with Sigma. False Assassin attacks Jester.
While they fight, Sigma suddenly has a flashback of a time a comrade named Lambda betrayed him during a mission and tried to kill him, only for Sigma to fatally wound him in self-defense. Lambda angrily said he had a cause worth fighting for and was even willing to kill his friend over it, while Sigma did not believe in anything, so why did Sigma win? Sigma simply said he didn't want to die. Then he went home and watched a comedy.
Sigma returns to reality and wonders why he had that flashback as he had never spared Lambda another thought. As he watches False Assassin attack Jester by summoning spirits called jinnīya, he realizes the look of anger and determination on her face matches Lambda's. He shoots Jester in the face, only for him to heal the injury and yell at him for interfering. Sigma telepathically communicates with Watcher and then recites several facts about Jester. Unnerved, Jester demands to know how he learned this, but he doesn't answer. Jester moves to attack him, but they are distracted when they sense True Archer's power and then they hear an unnerving roar. Alarmed, Jester says if this keeps up, everything will be destroyed. Jester then grins and says he'll move them to a new stage. Sigma and False Assassin are shocked when a wave of blackness washes through the hospital and then the street. When it passes, Sigma and all the other combatants have vanished, to the shock of those observing.
Sigma and False Assassin wake up in a garden covered by blankets and with pillows under their heads. He comments to himself that since Servants do not normally sleep, something must have rendered them unconscious. They assume Jester put them there and wonder why he didn't kill them while they were asleep. He then comments that some Magi are sadistic and fond of putting curses on their opponents and letting them go so they can watch them fall to the curse later. They examine themselves with their magical senses and find no curses on them. He then realizes he cannot hear Watcher nor sense their presence. False Assassin suggests summoning his Servant with a Command Spell, but he hesitates because he's not sure what would actually happen.
He checks his GPS and finds they are in the Snowerk residential area, a district of Snowfield. They are about to leave the garden when a man walks up and greets them, introducing himself as Mr. Kurouka. Sigma recognizes him from his files and asks what happened to them. Mr. Kurouka says his daughter found them passed out in their garden this morning. Mr. Kurouka's wife walks up and says their daughter gave them their blankets and pillows. False Assassin whispers to Sigma that the couple seem to be controlled by something.
The two are then shocked when Tsubaki, who is supposed to be in a coma, walks up and says she is happy they are all right, then introduces them to her friend, Mr. Black. They turn and look in horror as they see a cloud of blackness under a tree, despite Tsubaki assuring them he is friendly. 
As Tsubaki and Mr. Black leave the two to their own devices, they speculate on Mr. Black's true nature, as False Asassin was unable to sense any malice or energy from it. They wander the city and find a few people who seem to be survivors of an attack on a factory the other day, but though they can speak, they are under a form of mind control and don't have any answers. While False Assassin keeps a lookout. Sigma questions Mr. Kurouka in the park and says he knows he was hired by Francesca and Faldeus. While clearly under mind control, Mr. Kurouka says he gave up on the Grail War to care for his daughter. Sigma asks what is going on and Mr. Kurouka matter of factly explains that Tsubaki's Servant sent them all to another world, possibly a Reality Marble. He is happy and doesn't want to leave. Sigma warns him about how Tsubaki was threatened in the real world and the man says Tsubaki's Servant sent a guard dog and leaves despite Sigma's protests. False Assassin walks up and says she thinks Tsubaki's Servant heard them. She points him toward Tsubaki's house and he is horrified to see Cerberus, remembering the three headed hellhound summoned by True Archer. When before he was the size of an elephant, now Cerberus is larger than the house.
He was first mentioned in Fate/Zero novel. He was indirectly mentioned when Maiya confesses to Irisviel von Einzbern about being a mother. Irisviel encourages Maiya to look for her son after the Fourth Holy Grail War.
Sigma is a Spellcaster, excelling in the use of familiars. He is less of a mage, and more of a mercenary who employs magecraft to achieve his goals. He has been trained from childhood to become a soldier, making him very skilled in numerous weaponry and combat. Sigma is supposed to be the one to become True Lancer after summoning Watcher.
- ↑ 1.0 1.1 Fate/Zero - Volume 4: Act 13 -37:02:47, p.089-092
- ↑ 2.0 2.1 Fate/strange Fake Volume 4, Interlude: "The Trials Begin"
- ↑ Fate/strange Fake Volume 4, Interlude: "Watcher"
- ↑ Fate/strange Fake Volume 3, Extra
- ↑ Fate/strange Fake Volume 3, Interlude: "The Passion of the Nameless Soldier"
- ↑ Fate/strange Fake Volume 4, Interlude: "The Boy Does Not Believe In God"
- ↑ Fate/strange Fake Volume 4, Interlude: "Backstage at a Third-Rate Comedy"
- ↑ Fate/strange Fake Volume 4, Chapter 12: "The Gods Return from Twilight"
- ↑ Fate/strange Fake Volume 4, Interlude: "Parade of Treachery"
- ↑ Fate/strange Fake Volume 4, Chapter 13: "At Last, a Second, and a Third"
- ↑ Fate/strange Fake Volume 5, Interlude: "Mercenary, Assassin, Vampire I"
- ↑ Fate/strange Fake Volume 5, Interlude: "Mercenary, Assassin, Vampire II"
- ↑ Fate/strange Fake Volume 5, Interlude: "Mercenary, Assassin, "
- ↑ Fate/strange Fake Volume 6 Interlude: "Mercenary, Assassin, Pale Rider"