My Mangekyo Sharingan Can't Save My Hero Academia

So here's the pitch: I got reincarnated with Mangekyo Sharingan. Sounds overpowered, right? Instant win button? Except I can barely keep it active for thirty seconds without feeling like my brain's being microwaved. My chakra reserves are pathetic. My combat experience is zero. And the system that gave me these powers took one look at my situation and said “good luck” before fucking off into hibernation. Oh, and the Hero Killer—the guy who murders heroes for not being “worthy”—just decided my mom wasn't good enough. She'll never walk again. I know when he'll strike next. I know where. I've got exactly four weeks to train. Four weeks to go from “can't throw a punch without tripping” to “can survive a fight with a serial killer.” The smart move? Stay out of it. Let the pro heroes handle it. But I'm fifteen, angry, and apparently making life decisions with the wisdom of a shounen protagonist. At least I'm in General Studies. Low expectations. What does being a hero have to do with revenge anyway?