Sorry dabi is partially a what now-
Oh hello, yes, my tin foil hat is on and I’m going go force my dabi-is-partially-a-nomu-theory onto EVERYONE.
Let’s review what we know about Touya Todoroki:
Had a strong, fire quirk. Flames ran even hotter than Endeavors.
Body too weak for his own quirk, likely required a lot of medical care.
Father was distant/abusive/neglectful, mother had her own health issues and was put in the hospital herself, meaning his support system was weak.
Currently, his family believe him to be dead.
We don’t know exactly how he died, but we do know that Natsou blames Enji for it, and Enji now believes he was somewhat at fault too. Fuyumi seems on the fence about the whole thing, as does Shouto. This implies that Touya ‘died’ due to something happening, rather then say Enji killing him directly (accidental or on purpose), or even due to Touya killing himself.
So, we know that The doctor/AFO used hospitals to get strong quirks. They did not have a moral issue with using children for this, and they’ve been doing it for a long time.
Touya would’ve been a perfect target for them. A kid with a strong quirk, weak body, and nobody really protecting him? Hell yeah, Nomu time! Let’s assume Touya’s issues with his quirk were bad enough that they were willing to try experimental treatments.The doctor makes an offer that seems perfect for them, and boom, he’s got Touya under his thumb.
Since Touya’s treatment would’ve revolved around his quirk anyways, I think the doctor would use this chance to start trying some form of turning someone into a Nomu while they’re still alive. Maybe it’s a slower process, or maybe he’s just priming Touya to become a nomu, but I think that’d be what he’d do, under the guise of ‘strengthening Touya’s body to handle his quirk’. It’s the sort of treatment that means he has to basically live at the hospital though, making him rather isolated from his family.
Such a treatment would probably even appear to work for awhile, but before long, side effects start popping up. Touya notices them first, but he has a very hard time articulating what’s going on, and few people who would listen to him.
But, Enji does eventually visit and gets a bad feeling about the whole thing. It takes awhile, but he makes the call to pull the plug on the treatment when the side effects start getting worse with Touya. The Doctor tries to talk him out of it, telling him that stopping the treatment now could be very risky, but Enji stays firm and wants Touya home within a few days.
This means the Doctor has to accelerate his treatment plans, and he gives Touya an injection that’s meant to cause his quirk to go out of control and kill him so he can be turned into a Nomu but his death can be blamed on stopping the treatment.
Only... it doesn’t quite go according to plan. Touya’s quirk does go out of control, but by this point his body has already somewhat gotten stronger from the nomu treatments. It’s just enough that while he completely destroys the hospital room he’s in and does a lot of damage to his own body, but it doesn’t kill him. He also overheard the doctors or the nurses having a conversation, not enough for him to know everything, but enough for him to realize he isn’t safe here.
So Touya escapes, leaving behind the ruined hospital room. The Doctor assumes his quirk went too far out of control and that he’s now just ash, and he’s disappointed but he informs the Todoroki’s who are horrified. Natsou blames Enji for taking Touya off the treatment. Shouto is too young to really understand what’s going on. And Fuyumi is old enough to understand that the situation was complicated, and she can recall the negative side effects of the treatment enough that she’s able to understand why their father made that call to take Touya off it.
Touya, meanwhile, is left struggling to survive. The nomu treatments seriously fucked with his head, removing a lot of his moral boundaries, messing with his memories, and leaving him pretty unstable. However, they also make his body just strong enough to keep going, although it’s not strong enough to fully stand up to his fire. In the end, I think Touya decides his father must’ve tried to kill him because he was ashamed of Touya, which leads into him taking on the title Dabi and setting out to kill Endeavor.
Dabi also finds himself draw to Tomura, at least partially because of the small, nomu like part of his brain that’s programed to obey certain people. Despite this, Dabi is still able to disobey Tomura and act like he’s just a regular person.
That leads us into the current Nomus-are-people-arc, with quite a few possible routes. Maybe while raiding the hospitals, Endeavor finds his own son’s records in there indicating that he was subject to these treatments. Maybe Hawks is the one who figures it out, when he notices some odd behaviors with Dabi and the Nomu. Or maybe, Dabi finds out about the nomu and where they’re created, and he finds his own file in the nomu’s records. This leads him to turn on the doctor/the league, because he’s realized that they were the ones really responsible for what happened to him.
