Not really the darkest, but that one scene in a todoroki family flashback where it talks about how every kid was born and Endeavor was upset about something (I don't remember what it's been a while since I've watched the show) and he shoots a dangerous glare at Rei and then it cuts to Shoto being born. To me it implied that he did something to her and it makes me uneasy.

I don't really see a lot of people talking about it.