Kenichi Shirahama, a high school student, can be found either buried in self-help books or getting pummeled in karate club after school. One day, he unintentionally scares a new student named Miu Furinji while heading to school. In her defense, she throws him down but later apologizes and befriends him. After karate club practice, a club member challenges Kenichi for a fight, and the loser has to quit the club permanently. Feeling dejected, Kenichi witnesses Miu easily fending off three thugs and asks her for tips on improving his fighting. She directs him to her grandfather's dojo, Ryouzanpaku, where strange yet skilled martial arts masters hone their abilities. However, Miu issues a warning that Kenichi won't survive unless he trains hard. As a criminal martial arts gang known as "Ragnarok" threatens the safety of the people around him, Kenichi embarks on an arduous journey to become a world-class fighter and defender of the defenseless, haunted by the ominous words of surviving his training.