Shimura Family

Kotaro Shimura's loathing of heroes set the temperature in that house. His mother, Nana, had placed him in foster care because her work made him a target, and he never forgave it. Under his roof heroes could not be mentioned at all, and his son Tenko was beaten whenever the rule broke.

The rest of the family treated the boy well. His older sister Hana encouraged him, his mother Nao comforted him and pressed her husband to ease off without ever moving him, and his maternal grandparents Chizuo and Mako did what they could to keep him happy. What none of them did was intervene, and Tenko grew up afraid of his father. Abuse layered over that silence bred a misery that curdled into one conclusion: the home he was raised in dressed rejection up as kindness.

The end came the evening Kotaro discovered his children had been in his office and seen a photograph of him with his mother. Tenko was delighted to learn his grandmother had been a hero; Kotaro was enraged and punished him physically. Nao and her parents challenged him over it that night, far too late. Tenko's Quirk manifested in the dark outside, and by morning the whole family was dead and the house was rubble, all of it his own doing. All For One found the traumatized child afterward and groomed him into Tomura Shigaraki.

The memories did not survive intact. Tomura grieved at first, but once he recalled his father's abuse and his family's inaction, he turned the whole thing into fuel and aimed it at hero society. The revelation waiting at the end is that All For One engineered every piece of it, granting Tenko the Decay Quirk as a child and arranging his birth, upbringing, and family's death to cultivate a vessel that could one day seize One For All. Once Tomura fell during the Final War, nobody from the bloodline was left alive.

It traces to Nana Shimura, a professional hero active while All For One still governed Japan unseen, and the seventh holder of One For All, supported by her friend Gran Torino and her student Toshinori Yagi. She married and had Kotaro, and was content until a villain killed her husband. Terrified that All For One would use her son to reach her, she surrendered Kotaro to foster care and doctored the family register to sever every trace of the connection, leaving a letter promising she would love him beyond death. She died in her fated battle, handing One For All to her student while Gran Torino carried him clear of the fight.

Kotaro grew up certain he had been abandoned. He worked hard, became a successful businessman, married Nao Magi, built a large house, and brought her parents in to live with them. Hana was born first. He also befriended a man from Koga Constructions, never suspecting the friend was All For One himself, the one who had murdered Nana. Playing on Kotaro's contempt for heroes, the villain suggested a second child, since Hana was already too old for his purposes, and Tenko was born. While the boy was an infant, All For One stole his unformed Quirk, keeping enough distance afterward that nobody suspected a thing.

The manipulation ran for years, hardening Kotaro's rules until punishments escalated. Tenko adored heroes and played at being one with his friends Mikkun and Tomo, so those punishments landed on him constantly. One day All For One walked him home from the street, holding his hand and quietly gifting him Decay, a Quirk rebuilt to do nothing but destroy.

Then Hana showed him the photograph and encouraged his dream, imagining the two of them as hero siblings. When Kotaro found out, she panicked and blamed her brother to save herself. Kotaro told his son the woman in the picture was no grandmother but a monster who abandoned her child, then struck him and shut him outdoors in the dark. Grieving over his mother's letter that night, he was confronted by Nao and her parents and admitted he had gone too far. Outside, Tenko sobbed to the family dog, Mon, that he hated them all for letting it happen, and Decay finished manifesting. Mon disintegrated. Hana came out to apologize, screamed at the remains, and crumbled when her panicking brother grabbed her. His mother and grandparents died the same way. Kotaro came running, struck the boy with a garden tool, and that blow snapped something loose: Tenko killed him and levelled the house.

Nana Shimura stands at the head of the line and shapes everything after it. Giving up Kotaro was an act of love that became the wound producing her grandson, a mistake she acknowledged when she asked Izuku whether he could kill Tomura. His answer, that he had sensed a weeping boy inside the villain and that One For All was meant to save rather than kill, brought her to tears. During the Final War she met Kotaro as an adult, understood the pain she had caused, and held him while apologizing to him and to Tenko.

Kotaro Shimura is both victim and abuser, a man ruined by abandonment and then steered by the villain who caused it. Nao Shimura, Chizuo Magi, and Mako Magi were kind to Tenko and confronted Kotaro only on the last night. Hana Shimura encouraged her brother's dream and then framed him, a betrayal Tomura forgave when he met her again in his mind. Mon, the family dog, was the first to die.

Tenko Shimura became Tomura Shigaraki, wearing his family's preserved hands as a costume that sickened and soothed him at once. He recovered the memories during the Revival Celebration, crushed his father's hand, unlocked his true power, and used it to take the Meta Liberation Army and form the Paranormal Liberation Front. Only Nana's hand remained afterward. At the end he conceded that the weeping boy may have been real all along, asked Izuku to tell Spinner he never gave up on destruction, and passed away in peace.