The world of My Hero Academia is not simple, the characters in the manga are all flawed human beings, both good and evil exist within them. While we see villains with tragic pasts, we also see lawful citizens doing cruel and heartless things.
An example of both can be found in Shigaraki's backstory. Abused by his father throughout his childhood, little Tenko Shimura's life becomes a living hell when his Quirk awakens, killing everyone in his family.
In a terrible emotional state, he ran away from home. But no one on the street helped this lonely child. When an old woman asked about the child, she was immediately frightened by his appearance and hurriedly left without caring about the child. She had no idea that one day, this child would become Tomura Shigaraki and try to destroy the entire country.
After Shigaraki's death and the end of the war, the old woman reappears in My Hero Academia chapter 427. She is one of the citizens who hates Shigaraki and wonders if the heroes could have stopped him sooner.
Ironically, she could have been the one to stop Tenko from becoming Shigaraki if she had helped the poor child on the street back then. But she didn't and instead criticized the heroes who risked their lives to protect civilians like her.
After that, fans unanimously agreed that she was one of the worst characters in My Hero Academia. One person expressed: “Ironically, she wondered if Shigarak could have been stopped sooner, when she herself was one of the people who didn't help him in the first place.”
Another commented: “The butterfly effect, you never know what consequences your actions, or lack of actions, might have even years from now. I wonder what she would say if she knew Shigaraki was once a boy she didn't help.”
“I think the point of bringing her back was to show that you can be part of the problem too…”, a third commented, explaining the woman's role in the story.
Shigaraki's past is one of the most heartbreaking parts of the story. The return of the old woman reminds readers that no one is born evil, but instead evil is created from human cruelty and All For One's machinations.