Kyōsuke Yaguchi enters Morimori Academy as a first-year student, initially presenting as a popular and approachable classmate. He stands 165 cm tall with an athletic build, sporting shoulder-length caramel-brown hair typically tied in a small left-sided ponytail. His light brown eyes and slightly tanned skin enhance an outwardly friendly demeanor, often seen in the school uniform: white dress shirt, black sweater, red tie, and red-and-white shoes. Yaguchi cultivates an image of cheerfulness, kindness, and consideration—exhibited when sharing food with a peer who skipped lunch. This persona deliberately mimics his cousin, Yū Kashima, whom Yaguchi envied since childhood for universal admiration. Behind the facade, he is detached, arrogant, and prone to angry outbursts, privately viewing others as gullible for trusting his false kindness. His rivalry with Kashima fuels manipulation of transfer student Takashi Tōno, Yaguchi’s sole genuine friend. Upon learning of Kashima’s romantic interest in Tōno, Yaguchi resolves to "steal" Tōno as vengeance. During a school camping trip, a storm strands Yaguchi and Tōno together. Trapped in darkness—which triggers Yaguchi’s fear of ghosts and the dark—his panic shatters the constructed image. He reveals bitter envy toward Kashima, exposing his true self to Tōno. Yaguchi maintains a complex dynamic with second-year student Yui Tamura, who harbors unrequited feelings for him. While outwardly tolerating Tamura’s attention, Yaguchi privately demeans him, such as mockingly thanking Tamura for soccer advice while muttering insults. His hobbies include soccer, and his stated preferences are Japanese barbecue and ramen—contradicting earlier reports of favoring sweets, attributed to unreliable self-reporting. He dislikes carrots. Yaguchi’s actions throughout stem from unresolved resentment toward Kashima and the struggle to maintain dual identities. His background reflects persistent insecurity and performativity, constantly measuring himself against his cousin’s perceived superiority.