Akisame Koetsuji, known as the Philosophical Jujitsu Master, is a senior and one of the oldest masters residing at Ryōzanpaku dojo, where he also serves as the primary medical expert. He has above-average height, messy black hair, a meticulously groomed mustache he takes great pride in, and dull, nearly solid white eyes. His lean physique conceals muscles developed through decades of specialized conditioning, giving him superhuman speed, stamina, strength, and durability. Bullied in his youth, he pursued martial arts to prove his worth, traveling globally to refine a unique Jujutsu style incorporating elements from diverse combat systems. During his journeys, he befriended Saiga, Miu’s father, and encountered Shigure and her terminally ill father, a master weaponsmith. After reluctantly honoring the father’s request for a duel to die a warrior’s death, Akisame named Shigure and arranged for her upbringing, later bringing her to Ryōzanpaku. He also trained Ogata Isshinsai alongside Kensei Ma before Ogata’s expulsion. Akisame operates a renowned orthopedic clinic and has performed lifesaving surgeries under extreme conditions, earning him the moniker "The Medic Demon" among professionals. Despite a calm and rational demeanor, he is the strictest instructor at the dojo, employing grueling training regimens and designing machines that force disciples into unnatural positions. He detests green peppers and habitually scratches his mustache after lying. A defining trait is his unyielding stubbornness when uttering "Eh, I don’t want to," refusing compensation regardless of pressure. He holds a long-standing grudge against James Shiba, who mocks his mustache, a rivalry that culminated in a wager over their facial hair. Akisame is a polymath with expertise in philosophy, psychology, engineering, fine arts, and languages including Japanese, Russian, and English. His combat style emphasizes defense but can inflict severe harm, using ki to manipulate opponents without physical contact. He adheres to the principle that masters should not interfere in disciples’ battles but intervenes when masters threaten Kenichi directly.