Professor Todo

A professor at the university Yu and Kaito attend. An authority on combat science. A former Olympic silver medalist and Kyokushin Karate black belt. 49 years old. Interested in Yu's overwhelming strength, he invited Yu and Kaito to start a combat science seminar. He has a slovenly personality and is usually seen in a tracksuit. He quietly watches over Yu and Kaito's relationship. One of the few people who knows about Yu's past.

Mr. Okochi

The advisor for the Judo club at the university Yu and Kaito attend. A former Olympic gold medalist in the men's 100kg Judo division. 49 years old. Having heard from Professor Todo that there was an 'interesting guy' around, he showed a strong interest in Yu. He accepts Yu's tragic past and supports Yu and Kaito's relationship. One of the few who knows Yu's history. Terrifying when angry.

Leon Akagi

A red-haired professional MMA fighter. 26 years old. He has a flashy, playboy-like personality but is a kind person who cares deeply for his friends. He lost to Yu in an exhibition match. Since learning of Yu's tragic past, he has been a close ally and comrade-in-arms. He is also on good terms with Kaito and fully supports their relationship. Surprisingly, he is a great cook and has published a cookbook for athletes. He is part of a group chat with Yu, Kaito, and Kai.

Kai Kurose

A black-haired professional MMA fighter. 26 years old. Partners with Leon. He is a man of few words and can seem blunt, but he observes others closely. He acts as the brake for the impulsive Leon. He lost to Yu in an exhibition match. Since learning of Yu's past, he has been a supportive ally. He is friendly with Kaito and supports the couple. His hobby and specialty is sewing. He is part of a group chat with Yu, Kaito, and Leon.

Takuya Saeki

Kaito's father. An active-duty firefighter. 48 years old. He knows about Yu and Kaito's relationship and watches over them. He appears stoic and intimidating but is a father who cares deeply for his son. Despite knowing Yu's tragic past, he accepted the lonely Yu as part of the family.

Miyuki Saeki

Kaito's mother. A beautiful and kind woman. 48 years old. She fully supports Yu and Kaito's relationship. Knowing Yu's past, she welcomed him into the family with open arms. She is an excellent cook.

Yuto Saeki

Kaito's younger brother. A 10th-grade high school student. 16 years old. Handsome, much like Kaito. He has a bit of a brother complex and adores Kaito. He looks up to Yu as if he were his own biological brother. An honest and kind boy who supports Yu and Kaito's relationship more than anyone. Like his parents, he welcomed Yu into the family despite his past.

Tatsuya Takahashi

Yu's master and foster parent. Deceased. Died at age 78. The strongest figure in the martial arts world, having mastered every form of combat to the limit. A solitary martial artist who never took a single student or disciple—until Yu. He took Yu in from an institution at age three, trained him in all forms of martial arts, and raised him as his disciple. He passed all 300 of his original secret techniques to Yu, recognizing him as his sole successor.

Yashamu

39 years old. The man at the core of Yu's past, who once stabbed Yu in the back and left him critically injured. A cold and ruthless man who gained control over the entire underworld at a young age.