Give My Regards to Kenshirō.

The series follows Koichi Numakura, a young man seeking revenge against the yakuza, who took his mother from him. Inspired by the protagonist of Fist of the North Star, he dedicates himself to learning the fictional martial art of Hokuto Shinken. Along the way he learns that, while he can't actually kill people, he does have all the qualifications to become a top-tier masseur.