Byakuya was born into the Matou family during Zouken Matou's long patronage, and while he is listed in the registry as Byakuya and Kariya's father, there are records of him dating back to their great-grandfather due to Zouken being five hundred years old. Byakuya possessed some form of ability as a magus, but only his younger brother, Kariya, was suitable as the proper heir to the family in Zouken's eyes. Neglected throughout his childhood, Byakuya grew to resent his younger and more magic-capable brother. Kariya refused to be the heir and a pawn for Zouken's plans, leaving Byakuya with no choice but to become the next Matou family head.
He later met and wed a woman, noted for having an "inheritor" sorcery trait, and fathered a son, Shinji, with her. Shinji turned out to be void of Magic Circuits, causing the pure-blooded Matou line to finally collapse as of their generation. Due to Shinji being incapable of magecraft, he was an unworthy heir that only served to deepen Byakuya's disgraces. Due to their failure, his wife was thrown into the worms storage where she later died. Ultimately, Zouken elected to adopt Sakura Tohsaka as the new heir to the family. Byakuya was completely aware that he was not really the head of the family since everything was orchestrated by Zouken, but decided to try and live a comfortable and carefree life. However, the strain of living under Zouken's authority proved to be too taxing, and Byakuya took to drowning his stresses in alcohol.
As the Fourth Holy Grail War began, Shinji was sent overseas in the name of studying, but Byakuya had no legitimate reason to leave Fuyuki no matter how strongly he was against staying. He was occupied with the task of acclimating Sakura to the worms and training her to be worthy of becoming the next head of the Matou house.
Byakuya has blue eyes and curly blue hair that almost reach his eyes. His clothing consists of a disheveled white shirt and a black suit.
Considered a disgrace to the Matou family, Byakuya is a depressed, broken man who has turned to drowning himself in alcohol night after night. It can be said that his soul has been ruined since long ago, having forced himself onto a road of no return. He should be regarded as the eldest son and inheritor of the prestigious Matou house, the final remnants of a mighty bloodline that had begun a pilgrimage to seek the traces of the Holy Grail in the distant past. His true nature is that of a puppet of Zouken, allowing him to control everything from behind the scenes. He originally thought becoming the family head was not quite as much of a disaster because Zouken gave up on him long ago, so it was fine even if he was head in name only and that he hated magecraft. Zouken only let him take charge of low-importance, miscellaneous tasks, and the actual matter of succession was completely placed onto Sakura. The Matou assets being traded for a comfortable and carefree life was agreeable to him, but the stress he suffered caused him to use drinking to run from it.
He believes himself to have completed his task as the current head to near perfection. He thinks Zouken, originally planning only to observe the Fourth War, is simply playing around with Kariya as a toy, so he thinks of himself as the only one in the family walking on the right path. The state of his abilities does not matter, so he firmly believes that his is the only one that could truly connect to the future of the Matou house. This thought is accompanied by even more heavy drinking. He is disturbed by the fighting in Fuyuki, so alcohol is his crutch to keep living there while remaining calm. He is terrified of Berserker, thinking him to be black like a vengeful spirit, and uses more alcohol to numb himself to the terror. He normally drinks himself to sleep, so his remedy for being sleepless is to drink even more. He simply wants to forget anything happening outside and skip through the night as quickly as possible.
Byakuya blames Kariya for all the pressure he must face as the head of the Matou family, having pushed the cursed destiny carried by generations of the Matou onto him, but he is actually happy that Kariya took his place in the Holy Grail War. As the inheritor, it should have been his "duty" to act as a participant, forced by Zouken, but he feels that he has made the correct and logical attitude in comparison to Kariya, allowing him to say such a thing with his chest thrust out in pride. He cannot understand why someone who was disowned would return, and he does not want to understand. He holds no sympathy towards the pain and suffering Kariya is undergoing, as he willingly left and returned to such a fate. He never held much familial love for him in the first place due to his actions.
« Kariya? I don't know where that fool is! »
|(Byakuya interrogued by Kiritsugu - Fate/Zero, Episode 21)|
Byakuya spends the nights of the week of the Fourth Holy Grail War peacefully in the mansion, all while terrified of the events going on outside. If a night is peaceful, he resents it because no dangerous events the previous night means that dangerous events are more likely for the next night. Once again drinking himself to sleep on the night Berserker kidnaps Irisviel von Einzbern while disguised as Rider, he is assaulted by Kiritsugu Emiya, having seen through Kirei Kotomine's plan due to Waver Velvet's ineptitude making it unlikely that he would find the location of their hideout.
He is immediately sobered by Kiritsugu pouring ice water all over his head, but the man's mere presence terrifies him to the point of extreme, voiceless panic. Seeing his eyes is enough to make Byakuya surrender any will to resist or uncover Kiritsugu's origins, as Kiritsugu is the very horror he was trying to forget with alcohol. Kiritsugu asks about Irisviel's location, and Byakuya is crushed with despair upon realizing that he cannot answer. Kiritsugu calmly takes out a gun and shoots off Byakuya's right hand, and upon there being no answer, determines that Byakuya knows nothing. Due to his broken nature, Kiritsugu believes he was the final straw that broke the camel's back. Byakuya will do anything to remove his present pain because he has reached a point where even betraying Zouken is acceptable, meaning that everything he says is a guaranteed truth. Kiritsugu was certain that only the Matou family could have kidnapped her, so he muses over the possibilities of where they could have taken her and the possible emergence of another force that could have taken her, all while not even bothering to look at Byakuya sobbing with pain and terror, before leaving the mansion.
In the anime, he asks about Kariya's location, to which Byakuya answers that he knows nothing about where Kariya is other than that he left the house with a man who claimed to be the overseer of the church. This little bit of information is enough for Kiritsugu to pinpoint Irisviel as having been kidnapped by Kotomine.
Byakuya died three years prior to the events of Fate/stay night and is only mentioned in flashbacks.
Unlimited Blade Works
Shinji briefly reminisces about him and his mother in the worm pit. He believes that Byakuya decided to willingly kill off their bloodline by not choosing him as the heir. He was told nothing of the truth of their lineage by him, and he believes that Zouken truly wishes for him to be the heir after having been later told the truth. He has no feelings towards his father because of that, believing that all his father taught him was existence and failure. He does not think of what his mother gave him, only that what is left of her is likely to be at the bottom of the room.
During a mental breakdown, Shinji reminiscences about him. Byakuya kept him away from the truths of the family, to the point Shinji was unaware about the worm pit or why Sakura was adopted into the family. Eventually he found out the basement by accident, causing Byakuya to glare at him as if he were a nuisance with an attitude he had never before seen. Byakuya started to spend more time with Sakura afterward, and he took a defiant attitude towards Shinji due to no longer having to hide anything from his son. He died shortly after, causing Shinji to "take possession" of Sakura.
« ...You're lucky, Shinji. You are not required to use magic. Forget all about this book, go and live your life like normal people. Do you understand? »
|(Byakuya trying to convince Shinji to stop pursuing magecraft - Heaven's Feel, Chapter 20)|
In the manga version of Fate/stay night (which follows a fusion of the Fate and Unlimited Blade Works scenarios), Byakuya is the head of the family instead of Zouken (who is absent) and he is the one who masterminded Sakura's adoption and training. Shinji was kept from the truth of magecraft entirely, and he only learns of it after following his father into his study. He learns the truth of Sakura after overhearing a conversation between her and his father, causing him to start abusing her. Byakuya's fate is unknown.
The Heaven's Feel manga adaptation shows more about him. His lost his hand after his encountering with Kiritsugu and apathetically went with Zouken's orders to train Sakura. His interactions with Shinji show that he was an aloof father and was very adamant about his son not getting involved in the affairs of the Matou magecraft. He was actually relieved Shinji was born without magic circuits, wanting him to live a normal life instead.
« ....What do you want, Shinji? »
|(Byakuya after Shinji finds the worm pit - Heaven's Feel Lost Butterfly Drama CD)|
Byakuya, Kariya and Zouken, are mentioned by Shinji in Fate/hollow ataraxia, calling them "terrible people".
In the Heaven's Feel II: Lost Butterfly drama CD he's mentioned in Shinji's flashbacks as his aloof father who didn't want him involved in the family affairs.
Byakuya has negligible ability as a magus, being inferior to his younger brother, and Zouken does not even consider him worthwhile at all. He does not have the mana level to sustain a Servant, and he was not deemed worthy by the Grail to receive Command Spells. He has a low amount of Magic Circuits, and his abilities are only good enough to defeat a small child due to Zouken teaching him barely anything.
Creation and Conception
Byakuya was originally not meant to appear within the story of Fate/Zero, and his only role is a brief appearance and quick exit. During the original draft of the scene in the fourth volume, it would have ended with “Kiritsugu visited the Matou house while searching for Irisviel, but it was useless.” Gen Urobuchi thought that “there isn’t enough violence today”, so Byakuya was sacrificed by being put on the stage.
 Fate/Zero material - Encyclopedia: Matou Byakuya [Person's name], p.104-105
Byakuya Matou [Person's name]
The father of Matou Shinji, our glorious wakame.
As a magus, he was inferior to his little brother Kariya, but because Kariya refused to continue learning magecraft and ran away, he had no choice but to become the next Matou family head.
But for Byakuya that was not necessarily a disaster, as Zouken had long ago given up on Byakuya and had taught him barely anything, and at most let him take charge of low-importance, miscellaneous tasks. Instead, the matter of succession was completely placed onto his adoptive daughter, Sakura.
Regardless of the fact that he was head in name only, or of his hatred towards magecraft, the Matou assets as a trade for a comfortable and carefree life was not too bad of a deal – or so Byakuya thought, as in the end he suffered much stress, and spent his days drinking to run from it.
During the fourth volume, he finally made his appearance & exited in a flash. Originally, the scene should have ended with “Kiritsugu visited the Matou house while searching for Irisviel, but it was useless.”. But because the author thought that “there isn’t enough violence today”, Byakuya, who would never have appeared in the first place, was sacrificed by going on stage. What a sorrow