Kotaro Shimura

"Do you really want to know what heroes are?! They're people who hurt their own families... only to help complete strangers."

- Kotaro ranting about his belief about heroes.

Kotaro Shimura is a deceased character in My Hero Academia. He was the son of Pro Hero Nana Shimura and the father of Tenko Shimura. Fuelled by his bitterness towards heroes, he abused his family harshly for even mentioning them, which was one of the factors that led to his son to become the villain now known as Tomura Shigaraki.

Personality
Kotaro used to be a happy and normal child until his mother gave him up to live with foster parents. This led him to resent heroes, believing them to be selfish individuals who abandon their families. He became an abusive parent towards his children, punishing them for mentioning heroes by forcing them to sit outside the house until they apologized. Kotaro is also resentful towards his mother for abandoning him in the first place, as seeing a photo of her enraged him and caused him to snap at his family while expressing his cynicism towards heroes.

Despite this, he does feel remorse after his breakdown, tearing up while believing that he went too far and not understanding why he snapped like that, especially after seeing his happier childhood. However, when he sees Tenko panicking after killing his loved ones with his uncontrollable Quirk, Kotaro panics and attacks him to stop him from getting out of control, a rash decision which ultimately leads him into being killed by his vengeful son.

Synopsis
When Kotaro was young, his mother Nana Shimura abandoned him to pursue her career of heroism, which drove him into hating heroes. Although he was successful enough in his job to build a home, his resentment never faded even after having his children Hana and Tenko, and he wouldverbally abuse his family to the point where all of them were scared of him. Tenko had a fascination with heroes, but this caused Kotaro to punish him routinely. However, he still had the support of his mother Nao and his sister Hana, whom showed him a picture of their grandmother Nana.

When Kotaro found out, he snapped at Tenko while the rest of the family only watched in horror, before forcing his son to sit out in the dark. Tenko breaks down in tears for all the abuse that Kotaro put him through along with his family's inability to help, and finds comfort with his dog until he accidentally kills it when his Quirk, Decay, manifests for the first time. Later, Hana tries to apologise to him for not standing up to him (as she was also afraid of what her father would do to her), but flees when she sees her brother unable to control his destructive powers. After the horrified Tenko accidentally kills his sister and mother with his Quirk, Kotaro sees his decayed family and attacks him in response. This leads to Tenko losing all of his sanity and love towards his family as he deliberately decays his father along with the house he built.

The only part of Kotaro that remained was his hand, which the newly-christened Tomura Shigaraki wore on his head as his new villain costume. Tomura repressed his memories of his family until his fight with Re-Destro, in which he remembered back when he was an innocent child with a caring family. However, he also remembers his father, the person who was cruel to him throughout his life, which causes Shigaraki to nullify all of his love towards his family and become more determined to destroy everything.

Trivia

 * The circumstances that led to Tomura becoming a villain (being abandoned by his family and rejected by bystanders) are exactly like Kotaro's past, leading to Tomura ironically becoming just like his father, only to a greater extent. Both of them took out their rage and disillusionment towards heroes and society out on others, but Tomura goes far enough to outright destroy them.