Red_Saber

Kairi Sisigou receives a shard of the Round Table from Rocco Belfaban to act as the catalyst for his Servant. Upon arriving in Bucharest, Romania, he chooses the cemetery in Stavropoleos Church for his summoning ritual. Due to the general nature of the catalyst, he has no idea as to which of the Heroic Spirits connected to it will be summoned, and at around the same time as the Black Faction summons their remaining Servants, Saber is brought into the world. She refuses to shake his hand when he introduces himself, initially displeased by the location in which she was summoned. As she deduces his status as a necromancer, they banter until he asks about her true name.

As she is wearing her helmet, Secret of Pedigree, he cannot see her statistics clearly even though he is her Master. After she removes it, his clear shock at her being female causes him to remark on it, earning a murderous gaze from her. As he promises to never again bring it up, she is somewhat placated as he moves back onto the topic of her name. She is confused because he should know from having called for her, but learns that it was a shard of the Round Table that was used. Her regained mood once again gone, she slashes it apart and stomps on it with pure anger towards it in her voice. This act allows him to deduce her identity, causing her to feel some shame at it being discovered from such actions.

They discuss her rebellion, which she speaks of with great rage and animosity. As her pedigree as the child of Morgan was too great a flaw, she claims she let the country end in rebellion to let all others see there was no meaning to King Arthur's reign. As she speaks of her wish, Kairi sees the flaw in that it is not guaranteed even with her bloodline that she will be able to draw the sword, but the certainty in her words causes him to think that she may even be able to easily draw it out. Saber then immediately decides that it is time for them to act, and as Kairi attempts to dissuade her from acting without knowledge, they are given a message from one of Assassin of Red's doves to arrange a meeting.

As they proceed towards the church in Sighisoara, Saber brings up the topic of clothing to wear in public, surprising her Master at the unexpectedness of the request, and he agrees to purchase them after the meeting. Arriving at the arranged time of nine in the morning, they are greeted by Shirou Kotomine, and though Saber cannot sense other Servants, she warns Kairi that she has a bad feeling about the situation. As Kairi and Shirou introduce themselves, Shirou asks for Saber to be materialized, and when Kairi starts to object, she tells him to proceed due to her feeling of unease. She appears on guard, and due to her Secret of Pedigree, Shirou is surprised when he cannot tell her statistics using his Ruler-class abilities.

After Shirou has Assassin materialize, Saber is angered at her presence, thinking her to be a "foul hag." As Shirou and Kairi speak of the strength of Lancer of Red and Rider of Red, Saber momentarily thinks that one could potentially be her father. Kairi dismisses the thought, hoping that their forces won't be divided from the very start by such an event. She is annoyed by Shirou requesting her true name to be revealed, but notes that Assassin's laughter bothers her even more. Completely against the idea on instinct, she is pleased that her Master is of the same mind. As they leave, she cannot sense any followers, and compares Assassin's treacherousness to that of her mother. Pleased with the personality of her Master in not placing a price on possible trickery and deceit, she claims that facing all of the Servants alone is nothing for her who was the only knight to surpass her father.

Kairi buys her clothing before they depart to Trifas, allowing her to stay materialized. She once again displays great eagerness to jump right into battle, but Kairi manages to dissuade her. Upon arriving at the location for his workshop, she is disparaged to find it to be catacombs. Although she tries to argue, saying that even if she had not been a knight that the location is unsuitable for anyone, he simply passes it off by giving her the better of their two sleeping bags. Realizing that arguing is worthless, she follows the adage of "the key to dealing with a magus is to give up." Conceding that it is a suitable location despite it being a tomb, she watches as he begins to process his hydra into a poison. Disinterested in the process, she asks about his wish for the Grail.

She finds his answer to be boring, but is somewhat upset when he brings up that sons looks to succeed the dreams of their fathers. Going to sleep, Kairi muses over her past and becomes slightly depressed upon seeing that she has the face of an innocent child as she sleeps. Upon searching for a suitable vantage point to scout the Black Faction's fortress, they trip a detection field and become attacked by Caster of Black's golems and homunculi. Fighting with her characteristic wild style of fighting, she easily destroys golems while Kairi fights the homunculi. Impressed with his abilities, they examine the remains of the golems, getting some idea as to their maker and a possible identity. They decide to retreat for the moment, and though they had been watched, Secret of Pedigree protected her identity. She inquires how he rates her abilities, proudly boasting at his praise.

She later fights with the shapeshifted Sieg who takes the form of Saber of Black during a large battle, she was disappointed with his strength as a Saber-class Servant and even pointed out that Saber of Black was a fake. After numerous clashes, he decides to utilize his Noble Phantasm Balmung, and she responds with Clarent. She emerges victorious, but only due to the special properties of the weapons and the distance from which they attacked. She is angry with the fact that he managed to survive, enraged by the unforgivable fact. Simply continuing to grip his sword is enough to earn her hatred, and raising his head and attempting to stand is something she could never accept even if given the chance to slash him apart a hundred times. She decides to lop off his head and run her sword through his heart, a privilege only allowed for her.