Koukin Shuuyu, a Nanyo Academy student and cousin to Hakufu Sonsaku, acts as her initial guide upon her enrollment. Initially a secondary figure, he rises to join the academy’s Big Four following Kōha Kannei’s defeat, securing authority within Nanyo’s power structure. Tasked with conflict mediation and tactical counsel, he prioritizes strategy over direct combat, relying on intellect rather than physical prowess. A pivotal moment in his arc occurs when Hakufu saves him after a brutal confrontation, purging malignant chi from his body through an unorthodox ritual. This transfers the corrupt energy into her own form, imprinting a permanent scar on Hakufu and exposing Kōkin’s susceptibility to external manipulation. His characterization shifts across adaptations: the manga frames him as politically shrewd, entangled in his mother’s covert efforts to steer Hakufu’s future. The anime strips these machinations, instead highlighting his supportive demeanor and sporadic comedic moments. Manga-exclusive threads hint at strained maternal ties, with his mother aiming to exploit Hakufu’s power for personal ambition—a subplot absent in animated versions. Later narratives and spin-offs reduce his prominence, sidelining him during critical events like the *Xtreme Xecutor* tournament. His role stagnates, serving primarily as Hakufu’s emotional anchor without substantive personal growth. Spin-offs and OVAs preserve his established persona as a steadfast yet marginal ally, adhering to his original narrative confines.