Akisame Koetsuji, known as "The Philosophical Jujitsu Master," is a senior and one of the oldest masters residing at Ryōzanpaku dojo. He possesses above-average height, messy black hair, a distinctive well-groomed mustache he takes great pride in, and dull, nearly solid white eyes. He typically wears a hakama, and his lean physique conceals muscles developed to perfection through decades of specialized conditioning. Bullied in his youth, Akisame pursued martial arts not for revenge but to prove his worth. He traveled globally to refine his unique Jujutsu style, incorporating elements from diverse combat systems. During these journeys, he befriended Saiga (Miu's father) and encountered Shigure and her terminally ill father, a master weaponsmith. Shigure's father requested a duel to die a warrior's death. Akisame initially refused but ultimately fulfilled the request after being forced into combat. Before dying, Shigure's father confessed his true intent was to set a negative example for Shigure. Akisame subsequently named Shigure and arranged for her upbringing under the master of the Kōsaka-style. After that master's passing, Akisame brought Shigure to Ryōzanpaku. He and Kensei Ma also trained Ogata Isshinsai before Ogata's expulsion due to concerning tendencies. Serving as Ryōzanpaku's primary medical expert, Akisame operates a renowned orthopedic clinic treating severe injuries deemed untreatable conventionally. His medical skills, including performing lifesaving surgeries under extreme conditions like mid-flight operations, earned him the moniker "The Medic Demon" among professionals. He applies his deep knowledge of anatomy and physiology to develop innovative physical conditioning methods. Despite a calm and rational demeanor, Akisame is the strictest instructor at Ryōzanpaku, employing grueling and often brutal training regimens. He designs elaborate machines to force disciples like Kenichi Shirahama into unnatural positions, leading to recurring escape attempts. He exhibits occasional anger, particularly toward masters who endanger disciples, such as Ogata's lethal training of Ryuto. A defining trait is his unyielding stubbornness when uttering "Eh, I don't want to," refusing compensation or demands regardless of pressure. He holds a longstanding grudge against James Shiba, who mocks his mustache, escalating to a rivalry where they wagered their mustaches on a duel between their disciples. After Kenichi's victory, Akisame ordered Shigure to shave all body hair from Shiba when he only partially complied. He detests green peppers and habitually scratches his mustache after lying. Akisame's martial arts expertise centers on Jujutsu and Aikijujitsu, making him a globally recognized Judoka. He masters both ancient and modern forms, including hybrid styles like Combat Sambo. His combat style emphasizes defense but can inflict severe harm when necessary, using ki to manipulate opponents without physical contact. He possesses superhuman physical prowess from 20 years of research and training, achieving peak balance of speed, stamina, strength, and durability through specialized "pink muscle" development. This enables feats like overpowering larger opponents or straightening bent street poles with a finger. Beyond martial arts, Akisame is a polymath with expertise in philosophy, psychology, engineering, and fine arts like calligraphy, pottery, and sculpting. He invents training devices doubling as dojo utilities, including a treadmill generator. His genius intellect grants exceptional perception, allowing him to deduce hidden thoughts or distant events. He is fluent in Japanese, Russian, and English, and excels at strategy games like Shōgi and Go, having never lost. In battles, he rapidly analyzes opponents to formulate counter-strategies, often employing unorthodox tactics like using environmental objects for advantage. Throughout Kenichi's conflicts, Akisame adheres to the principle that masters should not interfere in disciples' battles, though he intervenes when masters threaten Kenichi directly. He mentors Kenichi during key events, protecting a Russian congresswoman from Alexander Gaidar and defeating Yami's "Spear of the East" in Okinawa. His protective instincts surface when allies are endangered, such as vowing retribution against Yami after Shigure's injury during the Eternal Sunset plan. He provides critical medical aid to characters like Apachai Hopachai and Ukita after life-threatening injuries.