Hiroki Sajyou is a magus from a prominent foreign magus bloodline. He seeks the Root just like any other magus.
At some point in the past, he marries his wife (who is from an English background), who then gives birth to his daughters Manaka and Ayaka. His wife soon dies some time after creating her botanical garden, "Garden", due to both having a weak constitution and additional leftover strain from Ayaka's birth.
Hiroki Sajyou is a strict man who maintains a strict bearing towards his daughters on the surface. But, in truth, Hiroki deeply loves both his wife and his daughters and later shows regrets that he couldn't raise them better. Additionally, despite initially appearing to favor Manaka more, he insists in one of his journal entries that he loves both of his daughters equally and could never choose one over the other.
Prior to his wife's death, Hiroki was also a much more emotional and affectionate man, but after his wife's death, he returned to the mindset of a magus in order to deal with his grief. Hiroki later admits though that he regrets the decision, because it left his daughters with feelings of loneliness and minimized his function as a parent.
During the war, he displays weird behavior as a possible result of either Manaka manipulating him or of his growing awareness to Manaka's dark side, and becomes deeply disturbed and wary to the changes occurring in his daughter, Manaka. Despite this, he still tries to save both of his daughters, even though he ends up dying as a result.
Hiroki has dark brown and brown eyes. He is of fairly average height for an adult male.
Fate/Prototype: Fragments of Sky Silver Edit
In Fate/Prototype: Fragments of Sky Silver, Hiroki acts as a helper to his daughter Manaka throughout most of the First Holy Grail War.
At one point during the war, he takes Ayaka into Garden and explains to Ayaka that her mother had created Garden especially for her. He then tells Ayaka that Garden is hers from now on, and that she is to come here if something bad happens.
After Rider's defeat, Hiroki becomes aware of the changes occurring in Manaka and becomes wary of her manipulative actions as a result. He then spends much of the second half trying to figure out what Manaka is up to and trying to figure out the whereabouts of the Greater Grail. He also additionally pulls Ayaka out of school for a while and confines her at home in order to protect her.
At one point, Hiroki discusses his regrets over his parenting skills and concerns about Manaka with Saber. During the conversation, Hiroki also relays his concerns over Ayaka's future and her potential safety, if a second Holy Grail War should occur and jokingly suggests that Saber should become her protector. After Saber's conversation with Ayaka in her mother's Garden, Hiroki works with Saber to find the Greater Grail's location. Additionally, Hiroki also places protection wards in Ayaka's room to protect her from Manaka, though it fails and Manaka kidnaps her.
Prior to his departure to the Grail's location, Saber leaves a sacred relic with Hiroki. After discovering that Ayaka had been kidnapped, it is assumed that both Hiroki and Saber go to the Greater Grail's location together, in order to save Ayaka and stop Manaka.
At the site of the Greater Grail, Hiroki confronts Manaka and tries to stop her by telling her to stop using the Grail for her own selfish desires. Manaka rebukes his attempt and eventually he is forced to use force in order to stop her. This fails, however, when the Beast grabs Hiroki and smashes him against the cliffs. Hiroki later dies from his injuries in the hospital, right after telling Ayaka that she will have to participate in the next Holy Grail War.
Hiroki Sajyou utilizes an old style of black magic that requires the use of animal sacrifices.