Koetsuji Akisame is a central figure in the story as one of the senior masters of Ryozanpaku, a dojo that houses several legendary martial artists. In his late thirties, he stands at around 180 centimeters with a lean but perfectly conditioned build, the result of rigorous training with stone Jizou statues to develop explosive power and endurance. He is almost always seen in a hakama and takes great pride in his well-groomed mustache.

His martial arts are jujutsu and aikijujitsu, and he is classified as a Sei-type fighter aligned with the Katsujin Ken philosophy of sparing opponents. Beyond combat, he runs an orthopedic clinic adjacent to the dojo and is widely respected—and feared—in the medical community as the medic demon, capable of performing complex procedures such as the mid‑flight surgery that saved Apachai’s life. His deep knowledge of human anatomy and physiology underpins the unique physical conditioning methods he develops for his students.

Koetsuji Akisame is a man of many talents. He is a renowned artisan who has mastered calligraphy, painting, pottery, and sculpting. He also invents clever contraptions that serve as training devices for the dojo’s sole disciple, Kenichi, and as power sources for the building, including a treadmill generator. His intellectual range extends to strategy games like Othello, Shōgi, and Go, as well as computer skills, which he picks up with remarkable speed.

Personality-wise, he is the calmest yet one of the most intense of the Ryozanpaku masters. He possesses an uncanny ability to read people, often knowing what they are thinking or whether they are troubled, a skill that unsettles those around him, especially Kenichi. Despite his generally philosophical and controlled demeanor, he can be fiercely competitive, as shown in his ongoing rivalry with James Shiba, which frequently escalates into bets involving their respective mustaches. He is also a perfectionist and can seem inconsiderate toward his pupils’ feelings, though this stems from a sincere desire to push them beyond their limits.

His role in the story is that of the first master to agree to train Kenichi. He provides not only the foundational physical conditioning but also tactical and moral guidance, though he often argues that masters should let disciples fight their own battles. Over the course of the series, he evolves from a seemingly cold taskmaster into a mentor who genuinely worries about Kenichi’s safety, while still maintaining his rigorous training standards. He also acts as mediator among the other masters and brings a sense of balance to the dojo.

Key relationships include his old friendship with Miu’s father, Fuurinji Saiga, which deepens his protective instinct toward Miu. His dynamic with Kenichi is multifaceted: he is both an exacting instructor and a challenger who forces Kenichi to confront his limitations. His rivalry with James Shiba adds a layer of humor and shows his willingness to engage in light‑hearted competition. Within the dojo, he works alongside masters like Sakaki, often tempering the latter’s more aggressive impulses.

Notable abilities include his mastery of jujutsu and aikijujitsu, where technique is emphasized over brute force; his medical expertise that allows him to treat severe injuries and reset bones with ease; his innovative training methods and devices; his artistic craftsmanship; and his exceptional observational skills that let him read opponents and students alike. Through his combination of physical prowess, intellectual breadth, and philosophical insight, Koetsuji Akisame stands as a cornerstone of the Ryozanpaku group and a vital influence on Kenichi’s growth.