Evanescent

The world of heroes and villains was already complicated enough. It was just Izuku's luck to have gotten wrapped up in the underground element of society, monsters. However, it wasn't entirely his fault.

He was four when he was cursed with a quirk by his unsuspecting mother, who only had his best intentions at heart.

He was twelve the first time he encountered an actual monster for himself. He was still twelve when he accidentally killed his first monster.

By the time he was fourteen he was a highly successful vigilante and an elusive serial-killer--Monster Hunter. Which was alright, since he kept those two identities very separate.

When he finally turns fifteen he walks into U.A. aspiring to create a new identity as a hero and with the intent to keep his secrets six feet under. Izuku has a seemingly easy path to monster hunting retirement. It was too bad that the fates liked taking a gamble on when things would go wrong for him and how bad it would end up for him.