If selebus wants to make Yasu sex uncomfortable, he can just start it as a flashback with her doctor appointment.Rin pretty much offered to have sexual interactions with him with her wrist torn open, I can't see it ever being as uncomfortable as Io's stomachache. At most I think Rin'd be like "yeah, maybe that was a mistake" later, and move on.
Also, I mean, Makoto raped Akira during a depressive episode and I think a Rin sexual/depressive episode would mirror more of that than Io's.
I'm not sure about Yasu, but I also have a little difficulty seeing her in a traumatic sexual event without first having some character development that pushes her a little far from supernatural stuff. Otherwise, I'd be half-expecting her to not even remember it/assume it was god's command or something (like what already happened).
Hell to make it worse, the doctor could use the same words sensei use to convince yasu (or himself or player) for sex.