Quirk Singularity.
It’s been a thing throughout the entire series but people rarely talk about it.
Look upon your ultimate form, Shigaraki.
In an operating room, Ujiko gets ready to put Shigaraki under the knife, or laser, or whatever it is he’s gonna do bring out Shiggy’s full power. No, that’s wrong. He’s already at full power. Actually, Shigaraki wants to go PLUS ULTRA! Oh, the irony. Anyway, as strong as Shiggy is right now, he’s smart enough to know it’s still not enough to beat Japan’s heroes. Especially since Re-Destro survived their fight and his arm got damaged from using all his power. That’s where Ujiko, probably the most knowledgable person on quirks in the country or world, comes in.
So, back to Quirk Singularity. Ujiko explained the theory to Shigaraki. Basically, quirks are getting more powerful but human physical bodies aren’t keeping up. That could evenually lead to people developing quirks so powerful they can’t control them and they destroy the world. Bummer. Ujiko also said there have been actual signs of Quirk Singularity (or QS as I’ll call it from now on) since the Fourth Generation. What kind of signs? You should know. We’ve all seen it since the beginning. Not counting One For All slowly growing so powerful it can destroy it’s host body there’s Todoroki whose quirk can hurt his body if he doesn’t regulate his temperature, Kaminari whose brain fries if he overuses his electric quirk and Mineta whose head gets bloody if he pulls out too many grape balls. Tsuyu getting sleepy in cold tempetures, Aizawa needing eye drops, the list goes on. One things for sure, Horikoshi’s had QS in mind since Day 1.