He once tried fighting alone. Maybe he realized, that to change a culture and time, you need people who follow you. How do you gain people? Be nice to them and get them indebted to you. Also, he stopped plans of his adversary that included her being sacrificed. That is why he saved her. You are free to interpret things to fit your narrative. If you want to interpret it negatively and stop reading it without seeing the positive sight, it might be a waste :)
Who wouldnt save her if he knows that the damn girl is the sole granddaughter of one of his two best buddies?
I just hate her personalities. Gah! I really want to slap her face.
(╯°Д °)╯╧╧
I only got to chapter 12 but I cant even read it anymore... Him going to save that girl pisses me off. He is to kind hearted for me （￣へ￣）