I can't help but wonder what interactions between Kiel and either of my characters would be like.

I imagine Aoi and Kiel would hit it off decently, or at least have a good understanding of each other's mindset. They're both broken individuals; one's just had more time to deal with it and figure out how to be normal. Though, Aoi would probably be pretty awkward - imagine if you met someone so unlike you, yet you know that you could've ended up being this person pretty easily. Plus his sister's the guy's weapon, so there's that.

On Ilya's end... I have [i]no[/i] idea how that would end up. They're basically the exact opposite of each other. Though if Kiel takes after his father's dissection habits, there'd probably be some interactions regarding Ilya's unusually colored blood.