(Forgive the awkward wording, but I'm trying to be as un-spoilery as I can.)
In Episode 12 of Wonder Egg Priority, Ai hatches a Wonder Egg containing
herself from a parallel universe.
This girl's Wonder Killer takes the form of
Sawaki-sensei.
This suggests he did something that traumatised the girl and helped drive her to suicide, but it's never stated what. Furthermore, Ai spends the entire fight insistent that the Wonder Killer is based on her own cognition of that person, and not what they are actually like.
What did he do to her? And if he didn't do anything, then why was he her Wonder Killer?