Alright, this is gonna sound a bit weird, but I think the emotional tension there is almost entirely about distorted, obsessive mirrors. Deku is the ultimate altruist, built on saving people, and Toga’s love is a selfish, consuming thing that twists his ideals. The tension isn't just 'hero vs villain', it's about two totally incompatible understandings of affection colliding. Toga sees his willingness to get hurt for others and wants to own that, to drink it in literally. Deku sees her pain and wants to save it, but her version of being 'saved' is grotesque to him.
It creates this awful, fascinating push-pull where they’re both trying to connect across a chasm of violence. She thinks she's offering love by sharing blood; he thinks he's offering love by refusing to give up on her. Neither can accept what the other is handing them. That’ Trainer's a kind of tragic, messed-up stalemate that’s way more interesting than a simple enemies-to-lovers arc.