Hmm, this would certainly be a very difficult topic to cover. I will reluctantly agree it should be mentioned somewhere, but I'm not sure how it could be done tastefully. You mentioned the therapy sessions, I'd agree that seems like a good place to put something like this. The dynamic between MC and Asterion would have to be quite strong for the two of them to talk about something like this. Although I suppose that's true of the two of them discussing any of Asterion's past trauma.
Perhaps the developers will just say 'Nope Asterion has never been sexually abused' and then we won't need to worry about this at all, and can just ignore it?