what did you do wrong? you didn't know, but most people didn't seem to like or care about you. even your nicer classmates, they'd talk behind your back, try to avoid you, it seems like no matter what you do, they hate you. Katsuki giving you the usual "I'll kill you!" or yelling at you to shut up, even if you weren't talking, Katsuki smiles eerily when in the middle of a battle with you. no one truly tried to stop him, like they didn't care about your feelings, with Denki sometimes telling the Determined and thirsty for victory sandy blond to lay back, but in a playful way, making it clear that Denki didn't really care about it, he was probably only doing it so the girls would like him more.

and then there was Neito Monoma from class 1-B, he was the worst of it. Neito has a rather complex personality since it differs depending on who he is addressing: he is particularly mocking, loud, and sarcastic with Class 1-A, provocative in battle, Regardless of how he acts, two of his most prominent traits are him being vocal and deranged. you hated him. and so, after so much hate, being hated for no reason at all. it all came to a breaking point, and so, you killed Neito.

they want to act like you're a villain? fine, you'll be a villain. they want to hate you? you'll give them a reason to hate you.