I've read Ai dano Koi dano, Suna no Rasen, and Bannin already, and tried Tsuki Yadoru just now, and they don't have quite what I want in terms of regret. I'm looking for something more severe, like an "Oh god, what have I done" moment of horror, and/or a strong fear of touching the uke afterwards. I'll update the first post since it's a bit vague. ^^; Thank you!

Any more?

You are my prize in viewfinder in yaoi

That one has regret? o_o What part? I can't imagine the seme would actually feel any deep sense of regret based on his personality...

Bump

Quote from Blique

That one has regret? o_o What part? I can't imagine the seme would actually feel any deep sense of regret based on his personality...

I think the poster only read the "rape" part of your request. 🤣 Asami feel regret? 🤣 🤣

I think your difficulty finding titles shows how pervasive the 'rape is love' trope is. I only have one title to add to my original post, and it's just one episode in a larger story.
Tantei Aoneko - there's a scene of statutory rape, the boy is willing but underage. The MC feels guilty, to the extent that

he doesn't do it again, but he is still attracted to the boy.