So MC ambushed and killed someone for no reason, sure learn the technique, but there was no reason to take advantage of the dizzyspell to severely injure him, nor was there a need to continue chasing him after he had already learned the technique, it was unnecessary and something a villain would do.
so Mc sister has knowledge on swords. A man realized that and after she was attacked by a mental spell sue back mentally weak and very supceptible. A man then proceeded to use manipulation into getting answers about the swords. After getting the knowledge and not leaking his identity he kills MC sister. This is what MC just did to the guy. Hope you know if you pull the trigger on others expect it to be pulled on you.