So i don't know if you caught it but it was mentioned way back that saving the family name was the side motivation. His number one priority was to save his sister, who he assumed was alive all this time cause she was appearing in his dreams begging him to save her. Thats the real reason why hes doing all this. He was keeping the dreams of his sister stuff a secret and only advertised the saving the family name stuff since people would think he was going insane or being negatively affected by Kisaras demon energy