The following contains spoilers for My Hero Academia by Kohei Horikoshi.
A hero always tries their best to keep villains at bay, and always tries to keep society safe from those that would do them harm. Unfortunately, they forget to keep the people closest to them safe, especially from themselves. Enji Todoroki, better known as the Number Two hero Endeavor, is introduced in My Hero Academia as a negligent, abusive father towards his son, Shoto Todoroki. Before he's properly introduced, audiences already possess a negative perception of him. Endeavor had a long road ahead of him to build back his image with the audience, but more importantly, to rekindle a positive relationship with a family he tore to shreds.
Endeavor was always second best in hero rankings, living in the shadow of the world's greatest hero, All Might. He endlessly chased All Might's glory, desperately trying to claim the number one spot. Surpassing All Might's strength, however, proved to be an insurmountable task. Endeavor's Quirk, Hellflame, allows him to produce flames from his body. Endeavor reasoned that if he could create a child with his fire Quirk and a woman's ice Quirk, the two powers would create a perfect balance. The strength from the combined Quirks would give rise to a person capable of reaching number one. He arranged a Quirk marriage with Rei expressly for this purpose.
His other children were born with Quirks that were too weak to make them contenders for number one, until Shoto was born. He had the perfect combination his father desired, and at the age of five his training began. Shoto's training was brutal; Endeavor pushed him so hard he was sick every day from the stress and strain. Rei objected to his methods, but she was brushed aside and physically abused whenever she would intervene. One day, Rei snapped, throwing a kettle of boiling water on Shoto after he startled her in the kitchen, mistaking him for Endeavor. She was committed to a mental institution soon after by her husband.
Toya, Endeavor's first child, was born with an imperfect balance of Quirks, just like his brother and sister. His Quirk was more powerful than Hellflame, but his body could not withstand the heat as a result. Endeavor realized this, and stopped training Toya to focus on Shoto. Toya would train in secret, hoping to get his father's acknowledgment, but would end up consumed by his own flames. Thinking Toya was dead, Endeavor doubled his efforts on Shoto, training him even harder than before.
The Todoroki family was in tatters after these events. His children hated him, his son was presumed dead, and his wife had been mentally broken from his abuse. All the while, the public had no idea. To them, Endeavor was still a great hero, but those closest to him knew the truth.
It isn't until All Might lost his powers that Endeavor began to see the error of his ways. Becoming the new number one hero by default, Endeavor asks All Might what being the number one hero means. All Might tells Endeavor that filling his shoes will be impossible for anyone, and that he needs to do it in his own way, but not to neglect the ones closest to him like he did.
Endeavor began his attempts to rekindle his relationship with his family. Slowly but surely, he was able to reconnect with Shoto, and eventually Natsuo and Fuyumi as well. He never asked for forgiveness or understanding for what he did, but he tried to make things work anyway. Eventually, the family gathers to visit Rei in the institution, something they had never done before. Rei reveals to Natsuo that Endeavor had come to visit her many times before, but had never shown his face to her out of shame. Despite everything, Endeavor harbored deep regret for his actions, but his obsession with chasing the number one spot would never let him stop.
In the Paranormal Liberation War Arc, Endeavor learns that Toya is in fact alive, and has been the villain Dabi all this time. Now a twisted mass murderer, Toya reveals the Todoroki family secrets to the world in an attempt to destroy Endeavor's career as a hero. He succeeds, and the public outrage is enough to force him to come clean. Endeavor doesn't hide or shy away from the truth. After reestablishing his connection with his family, he is encouraged to own up to what he did. He confirms everything Toya said to be true, and instead of seeking forgiveness, he simply says that he will fight until his last breath to ensure that he fixes everything.
Though Endeavor's introduction paints him as anything but sympathetic, his redemption arc is genuinely a heartwarming one. Endeavor never shies away from what he did, and is unafraid to own up to the truth. While he can't change what happened, Endeavor does everything he can to atone for the sins of his past.