Board Thread:Questions and Answers/@comment-33181604-20170925092856/@comment-26500386-20170925095018

They're called theories for a reason - We have no idea.

Assuming they ARE, my biggest question is how the hell Dabi has black hair when todoroki's is red and white - Mix them together, you'd get pink, and Dabi doesn't even come CLOSE. Granted, since we're talking about a universe where literal superpowers exist, I'm not going to be surprised if genetics aren't the exact same. (Todoorki's hair is exactly half and half, for Gods sake, thats proof enough)

I do find it unlikely though. If he were, why wouldn't Todoroki mention it? He has no stake in his familys reputation, he doesn't care, and knows he wouldn't be blamed for his brothers actions. Why wouldn't he reveal Dabi to be his brother? Unless he doesn't know.

Again, unlikely, since if he didn't, that implies Endeavour has been having kids for well over 16 years. And he wouldn't be able to financially support that. He could send lots to an orphanage, sure, but I doub't Shoto's mother would be able to withstand all of that, and it's shown that they only looked after five kids. So that to me implies that no, Dabi isn't a Todoroki.

again though, we dont know.