Not too sure about first one but I believe the demons are some kind of amalgamation of man and machine. I think the mc is either what the demons were meant to be but somehow got corrupted (as in a perfect synchronization of man and machine working together in harmony) or that the mc is what all the demons were at some point before the ai they had in them started altering their bodies in unforeseen ways. And because the mc was in hibernation, these negative effects have not yet occurred between him and his ai. I suspect the mc might also be more akin to a cyborg and so the demons being corrupt versions of this makes sense to me if I'm correct.