Mahiru Seki, a former classmate and childhood friend of Kou Yamori and Akira Asai, grew up in a family running a flower shop. Once dreaming of inheriting the business, his aspirations soured under emotional neglect after his older brother Shougo’s death. His parents, particularly his mother, fixated on Shougo’s memory, preserving his room untouched since childhood and restricting Mahiru’s experiences—denying school trips with the claim his brother "wasn’t going." This neglect bred simmering resentment and depression, concealed behind a facade of schoolyard popularity and charm. Beneath his sociable exterior, Mahiru grappled with isolation, sharing authentic bonds solely with Kou and Akira. A turning point arose during flower deliveries for his family’s shop, where he encountered Kiku Hoshimi, a vampire. Captivated by her empathy, he sought refuge from his stifling home by pursuing vampirism under her influence. Kiku’s presence warped his demeanor, fostering aggression, cruelty, and an obsessive loyalty to her. This transformation fractured his friendship with Kou, escalating to violent clashes and a temporary rift. Mahiru’s turmoil deepened when Kiku disclosed her imminent death, compelling him to prioritize her desires over his own survival. Though initially ensnared by her supernatural allure, fragments of his former self endured—he secretly safeguarded a photo of himself, Kou, and Akira despite Kiku’s orders to burn it. Reconciliation with Kou emerged through a vulnerable apology and exchanged keepsakes, hinting at their enduring connection. Mahiru confessed his yearning to flee his family and a longing to reconnect with Kou and Akira, yet ultimately stayed by Kiku’s side. Kiku’s choice to become human by consuming Mahiru’s blood accelerated her aging and death. As a vampire, Mahiru’s existence hinged on Kiku, the sole figure he cherished from his mortal life. Her transformation and demise sealed his fate, her human presence lethal to him. Disintegrating, he apologized to Kou and Akira, his final moments echoing unresolved ties and resigned acceptance. His relationship with his mother stayed fractured. Years after her neglect, he confronted her, confessing past hatred before declaring apathy. A farewell letter disclosed initial vampiric intentions to kill his parents, abandoned in favor of a wish for their future happiness—without him.