Emi would make a perfect yandere.

Technically Toga isn't a Yandere. She's just a lovesick psychopath, she doesn't threaten people who hang around Izuku, she even had a small crush on Ochako or sm. She isn't a yandere.

Emi would be obsessed with Aizawa, hero or not, to the point it became obsessive and weird.

She'd actually make a horrifying villain.

It's proven her quirk is a radius quirk. When she activates it, it has a distance. That must mean she doesn't have control on who it hits. That's why she wore a mask in the Sports festival.

When you laugh to hard, you can't breathe.

She's literally choking you and you aren't even near her. She might be a whole twenty feet away and the heroes are choking. And that means they can't attack cuz their motor skills aren't working.

Ms.Joke could be a horrifying villain. Like society would be in danger if she was with the League instead of a hero.

People underestimate her and then they realize she doesn't have a limit on how much she can use it and her drawback is just being depressed.

Now think of villain Emi with a horrible crush on Aizawa. Like they met before she became a villain and she fell desperately in love with him before becoming a yandere and a villain.

Yeah bnha would probably extremely different with a literal side character having a different role. She's based on the Joker too so-

Emi: we live in a society
Aizawa: you literally chose to be a villain cuz I rejected you
Emi: W E L I V E I N A S O C I E T Y