I Also Have A Similar Theory. So We Know Shigaraki’s Dad (Nana’s Son) Was A Shitty Dad, And Is Maybe

I also have a similar theory. So we know Shigaraki’s Dad (Nana’s Son) was a shitty dad, and is maybe dead because of Shigaraki, but we don't know his quirk. We'll come back to him later. Now back to Nana. I can't put a picture here now, but Nana looks VEEEEEEEERY Similar to another character: Momo Yaoyorozu.

Like i said earlier, we dont know the sons quirk or Nana's, and we also don't know much about Shigaraki's past. so I think that the son got married to a rich woman and took her last name and they had 2 kids, a couple of years apart (and who knows? If The son died before Momo was Born, her mom could've re-married to avoid who-is-my-dad questions from baby Momo) the first kid, Shigaraki, and the second, their daughter Momo. And Momo doesn't know because her mom doesn't want her bubbly daughter to know her dad isn't really her dad ('cause that can be traumatizing).

But this is all just a theory I've had in my mind. I could be completely wrong and Momo and Shigaraki could have nothing in common at all.

(But side note: How ironic would it be if a couple had two kids with completely opposite quirks, Creation and Decay. But then again, that could be part of the Dramatic Plot Twist TM)

It’s stated that Shigaraki is Shimura Nana’s descendant. Also, they say that Nana didn’t want to All Might and Gran Torino to be in contact with her children after her death. Shigaraki Tomura is an orphan. Inko, said by All Might, “looks like Nana”. What if Inko was also an descendant of Shimura Nana? WOULD THAT MEAN THAT IZUKU AND TOMURA ARE RELATED?

My opinion: This could be a way of interpreting All Might’s statement. However, I think he was implying that Inko is beautiful and radiates a motherly vibe- both of which are true, btw

All Might is probably just admiring the way Inko takes care of Izuku as Nana took care of him 😊(but if you give this info to Todoroki, he might just connect the dots the way OP did)

details about the theory competition here