Takehiko Henmi, stepbrother to Nanako Misonoo through his father’s first marriage, conceals their familial tie initially to shield her from past conflicts. Following his biological mother’s death, his father wed Nanako’s mother, a truth undisclosed until later. A graduate student at Gakuin University alongside Takashi Ichinomiya, he aspires to academic research in Germany.

Prior to the series’ events, he tutored Nanako and her childhood friend Tomoko at a cram school, fostering a bond that led Nanako to affectionately call him “Oniisama” in letters chronicling her life at Seiran Academy. Though their exchanges seem platonic, Takehiko recognizes their biological connection immediately upon learning Nanako’s surname, upholding secrecy at his parents’ request to spare her familial turmoil.

He once romanced Kaoru Orihara, a Seiran Academy student, until her breast cancer diagnosis prompted her withdrawal two years before the series. Despite their separation, lingering emotions and shared acquaintances sustain their link. His presence also intertwines with Fukiko Ichinomiya, who harbors unnoticed, unreciprocated feelings for him.

His friendship with Takashi Ichinomiya thrives on their contrasting natures—Takehiko’s reserved integrity offsetting Takashi’s rebellious charm—cementing his place within Seiran’s elite social spheres. As family secrets surface, his role evolves from Nanako’s mentor to confidant. Departure for Germany and eventual marriage to Kaoru in select narratives punctuate his arc, diverging between adaptations: the manga unites them after Rei’s death, while the anime leaves his romantic path unresolved.

His name, merging “military” (武) and “prince” (彦), echoes themes of duty and nobility. In his mid-twenties, his actions subtly shape others’ emotional journeys, unintentionally sparking Fukiko’s manipulations and sustaining Kaoru’s unresolved devotion.