With respect to my fellow commentors, it's not at all unusual for someone to freak out a bit whenever they take another human life. Not doing so is rather worrying, in fact. While Taishi was totally justified in what he did, that's not going to make the nightmares any less terrible. I find it quite believable that he's like this now, refreshing, even. The usual MC never feels any remorse, for anything. This guy not only is going through this PTSD, but acknowledges the huge age gap between himself and the FMC.
Speaking of Marl, is she seriously trying to justify her Cosby-ing the MC because of some busted-egg prophecy?
I'm just glad that the surviving assassin (and the number killed went from twenty to twelve?) didn't end up as part of the harem... yet.