Have you thought any more about switching up the intros for non-straight characters? Or at least removing the heteronormative assumptions (MC thinks Tsubasa is cute; blushes over his female summon’s lack of clothing)? Of course, if Touya really is just straight, then I suppose you don’t really want to get my hopes up before dashing them (which has happened in at least one other WIP, involving a very awkward first, and last, kiss).
I should note that I agree completely that characters should have their own sexualities (I even recently started a thread calling for more characters who were honestly gay, as opposed to just being MC-sexual for convenience). But I do think it’s generally easiest to have the majority of ROs (at least) being bi/pan- or MC-sexual.