Kotarō Hoshizuki, a 26-year-old Libra born October 13, serves as a disorganized school nurse and reluctant academy chairman, his turquoise hair and light violet eyes contrasting with a wardrobe blending clinical white lab coats, v-neck shirts, purple scarves, and apple-green jeans. A failed aspiration to medicine haunts him, rooted in guilt over Yui Mizushima’s death—a tragedy that shattered his belief in his worthiness of love or connection. Though he once saw Yui and her twin brother Iku as siblings, her unspoken romantic feelings, revealed only posthumously, deepened his self-blame, cementing his emotional detachment.

He warns others, like student Tsukiko Yahisa, against forming attachments to him, retreating into absenteeism and relying on her to manage his chaotic infirmary. Forced into leadership after his sister Koharu’s overseas departure, he dodges computer-related duties and shuns alcohol due to its swift sedative effect, guarding against vulnerabilities. Interactions with Iku echo shared grief over Yui, tethering both to unresolved history.

Though subtle cracks in his defenses emerge—occasional openness with colleagues or students—his core remains defined by guilt and self-imposed isolation, a man balancing fragile growth against the weight of a past he cannot forgive.