@Legion_01
On the one hand, I agree. His psychopathic original self is bland and boring. Some authors manage to transcribe the charismatic danger of a psychopath, this one doesn't.
On the other hand, I'm not a big fan of abilities or items that instantly alter people's identities. And, by extension, stories that use these. It feels lazy because it means the author can just rewrite a character at any time without having to go through character growth and giving them reasons to change.
Here, it feels like the author wants the cold and calculating mental strength of a psychopath, without the emotionlessness that goes with it. Instead of writing a complex character that manages to blend these two traits, he makes the character jump from one to the other as he wants without actually putting the work of character growth.
This line of story could have been done better (in my opinion) by making changes more progressive in both directions or making the charm spell a permanent part of his personality, only showing his original cold traits through flashback.
I hope this time is just him faking it, and the two will come to some degree of understanding without resorting to instant brainwashing again. Basically, making gradual changes instead of a lazy instant one again. After all, she doesn't seem to have ill intent towards him, so he could accept her - to some extent - when he realizes this.