Responses
Guess he has the most motivation, as he was rejected by his family of aristocrats but really the author hasn't fleshed things out enough so we can only speculate. His relationship with Ryan might add to his conflict though, as Ryan apparently weakens himself in order to boost Christoph's health and looks out for him the most. Maybe Christoph was "planted" in the house the same way Kyon was, no one suspects him yet and he is able to access the aristocrats food so could have poisoned Lucaon without raising suspision.
I've been thinking for a while that Christoph was the culprit. But now I really think so. That first attack and the way he killed the guy was just to suspicious. And then Lucion getting sick right after