@maxterdexter:
After reading the official release, I wonder, in a different upbringing, would Shiggy still manifest decay? Or if it had manifested on tableware or a teddy bear, would his family be able to get him to calm down?
I mean, the poor dog was the activation, and then it started running wild with each death pushing him harder and harder into madness, destroying those who he loved, then those who he resented, and then the one he hated.
He's placing society in the place of his mom and grandparents, as "inocent" bystanders, and the heroes in the place of his dad, as oppresors.
Yeah, Shiggy's abuse and those he love and trusted turning a blind eye sent his quirk into overdrive. I could see it activating normally on a small object when he got mad one day, but never against his family if he didn't hate them.
@RedGreenBlue:
Something I’ve been thinking is this: The people who really know how quirks work in this universe seem to be aware that the mental state of the user and their power are intimately connected. If Shiggy’s upbringing had been different, I’m pretty sure that his quirk would have manifested differently, too. It may never have actually caused decay and may have instead given him the ability to just separate things without breaking them or something like that. Like an awakened Buggy from One Piece or something.
The interesting part of this theory, I think, is that it makes hero training that much more important of a part of this society. Not only are the heroes training to be better at using their quirks, but they are probably training their hearts to make their quirks more wholesome as well.
Makes me think, though. What would happen if there was a villain with a memory manipulation ability? They could easily manipulate even the most righteous heroes into being mass murder weapons.
I think the quirk you get is the quirk you get. Good or bad influences don't matter. I wouldn't say a quirk determines the user's personality as a rule; we've seen both people whose quirks fit their personality (Bakugo, Shigaraki) and people who don't (Shinso, 13).
But, maybe a quirk influences a personality. For example, anyone with an explosion quirk is predisposed to be a hothead, but depending on their environment they may end up not being one. Of course, with Bakugo's mom as a parent, there's no way Bakugo wasn't becoming a hothead.