Kokin Shuyu is the cousin of Hakufu Sonsaku and a first-year honor student at Nanyo Academy. He is uptight, serious, and protective by nature, often acting as a guardian for his cousin after she and her mother move into his home. Despite his shy demeanor and preference to avoid unnecessary fights, he is a capable fighter, though his lack of confidence prevents him from reaching the higher combat ranks he is otherwise qualified for. He possesses the soul of the historical strategist Zhou Yu, which grants him a natural aptitude for tactics and planning. His primary motivation is to protect Hakufu, for whom he harbors romantic feelings, and he often finds himself dragged into battles because of her impulsive actions. He also has a close but exasperating relationship with Hakufu’s mother, who enjoys teasing him. Early in the series, he is one of the stronger fighters at Nanyo, but as Hakufu grows more powerful, his role shifts toward that of a strategist and supporter. He eventually becomes a member of the Big Four, the top fighters of the school, after the previous member is defeated. Other fighters, such as Kanu and Ukitsu, have expressed interest in him. Over the course of the story, he develops from an insecure and reluctant participant into a more confident and decisive figure, embracing his heritage as a reincarnated strategist and taking a more active part in the conflicts between the schools. In combat, he relies on his martial skills and tactical insight, using his knowledge of the magatama artifacts that power the fighters.