thinking about an AU where Todoroki Touya didn’t have his quirk-body incompatibility and tbh I think he could’ve end up the ideal ‘masterpiece’ of Endeavor’s imagining.
Fact is Touya was eager to be a Hero and was supposed to be raised to be one, eager to be strong and learn a bunch of ultimate moves, eager to be his dad’s heir and surpass All Might. Attend UA, become a Top Ten within years of graduation, be seen as an embodiment of Hero Society. Much like Endeavor too, he'll be confident to the point of arrogance, he'll hate being shown up, and he'll work hard to be the best Hero, though for quite a few wrong reasons.
Touya would have been a great Hero, tbh, quirk and attitude and indifference towards all the 'trash' Villains and savviness and all.
Something so smooth-sailing is boring though, so let’s thrown in the cracks that are inherent in the characters and the world:
+ Someone as selfish, self-centered, and power-hungry as Endeavor will meet his downfall one way or another. He said himself that he still wanted a child with the ‘ideal’ ice and fire quirk, so he probably would’ve pressured Rei to keep having kids and inevitably Shouto would’ve been born, even as Touya was also 'perfect'. I can see… Endeavor pitting the siblings against each other; I can see both kids fearful of losing his attention and praise; and I can see him letting ‘his’ ‘successes’ get to his head and fracturing the family once again with his neglect and favoritism. That can end up with two Dabis being formed, jealous and angry. Maybe three or more if the neglect/abuse cut Natsuo or Fuyumi as deeply as it had cut canon Touya. A whole family of Dabis out for Endeavor’s blood. Patricide as a family bonding activity.
+ Endeavor was never going to surpass All Might, and he was never going to get over this inferiority complex, which was only gonna get worse over time. He intensifies his training, and poor, adoring Touya would’ve done anything to keep up, putting up with a lot, trying to mimic his father as much as he can. Touya, for better or worse, has the exact Plus Ultra trait Heroes prize so much. He has his limits though, because he's human, and that’s a breakdown waiting to happen. (Also Rei doubtlessly would try to intervene and save Touya - not that Endeavor would’ve let her.)
+ Touya exhibits (big-five-model) neurotic tendencies even as a child, so that’s gonna be an issue when he’s under pressure or feeling his self-worth being threaten. It’s also a trait Endeavor isn’t going to be happy about, since it’ll be something he sees as a weakness. Another recipe for a breakdown and disaster.
+ One persistent trait about Touya/Dabi is that he seems to see himself in ‘completely different worlds’ from others - he considers himself above the trash. Not exactly a Heroic attitude, and also not something Endeavor would try to correct because he’s the one who taught his son that. It’s gonna bite them both in the ass.
+ I feel like almost all possible AU Touyas will have a big, ugly, maybe public nervous breakdown and possibly go ‘Villain’ depending on how much social cushioning he has once he falls.
This being shonen, of course, means Touya would’ve gone to UA as the Arrogant Prodigy just waiting to have his ass handed to him by a Shonen Protag Type. for some reason I want this to be Iguchi Shuuichi - nothing special, probably not even Hero-course, heteromorphic, weak-quirked loser underclassman, Iguchi Shuuichi. After that, Touya'll slowly change, and start the long journey of conceptualizing himself as something other than Endeavor’s kid. A mix of Bakugou and Shouto, maybe. A Neji type.