At 18 years old, Itsuki appears weak but he is actually a student with skills in Aikidou, a Japanese martial art focused on defense. One day, while walking, Itsuki finds himself surrounded by a group of criminals. However, he is able to fend them off on his own, much to the amazement of Murashige Ryouta who attempts to rescue him. Interested in Itsuki's strength, Ryouta becomes fascinated by Aikido and Itsuki himself, following him to his family's home.