Naoki Murakami, a third-year student at Hakodate Koyo High School, excels academically as one of the school's top performers, positioning him as a strong candidate for Tokyo University admission. He balances this intellect with notable physical attractiveness and athletic abilities. His romantic focus centers on classmate Haruka Mizuno, whom he observes during a tennis match, sparking an immediate and intense fixation. Despite habitual overthinking and social anxiety, he directly confesses his feelings to her. To his surprise, she accepts, initiating a relationship that unfolds amid mutual preparation for Tokyo University entrance exams, with the threat of only one gaining admission creating underlying tension.

Personality-wise, Naoki exhibits a dichotomy: He frequently overthinks social and romantic scenarios, spiraling into anxiety and worst-case predictions that manifest as visible nervousness. Yet he counterbalances this with decisive, bold actions in pressured moments, such as his impulsive confession to Haruka. His rapid-fire thoughts often lead to elaborate mental scenarios and misunderstandings.

Across adaptations, his character evolves notably. The OVA depicts a significant shift from a conflicted but likable student to someone engaging in repeated infidelity, maintaining concurrent romantic or sexual relationships despite Haruka's loyalty.

Socially, his friendship with Hayato Sano is marked by rivalry, particularly when Sano develops feelings for Haruka. To sabotage this, Naoki fabricates a story about Haruka having a serious illness. His desirability attracts attention from others, including Eri Suzuki, who pursues him independently of his relationship with Haruka.