Honestly, my stance on incest is that it's fine as long as there's not a significant age gap involved (like a parent/child situation) at which point it would also be pedophilia and thus actually a problem. But like, incest between siblings or cousins or whatever doesn't really bother me inherently; at that point it's just down to whether or not the actual relationship dynamics are healthy, just like any other couple. Thus why I really dislike Mei and Yuzu from Citrus, but some of the like, actually biologically related sibling ships out there don't bother me in the slightest, because the way they're actually written is healthy and wholesome.
Anyway, that whole discussion aside, this seems pretty fun. Part of me is kinda hoping that at some point it'll progress past this initial round of misunderstandings and develop the actual relationship, because Shio's sort of like, oppositional mindset and evident inferiority complex feels like it could go from funny to kinda grating if it gets dragged out too long, but at least at the moment I'm enjoying seeing this play out.
Kafka's definitely an interesting name for the other girl. Makes me think of Kafka from Arknights, though personality-wise she's very very different.