Natsuki Mogi attends high school as Takumi Fujiwara's classmate. She managed the school soccer club until an incident involving her then-boyfriend. After he boasted about coercing her into intimacy, Takumi punched him. Unaware of the reason, Natsuki stopped speaking to Takumi until learning the truth. Later, Natsuki entered a relationship with an older salaryman who paid her for companionship, evolving into a transactional sexual arrangement. Unknowingly, he was the father of her friend Shiraishi. She questioned the high payments compared to peers' earnings, but he reassured her of her worth. Natsuki reconnected with Takumi, organizing trips to Kashiwazaki beach and Lake Akina drives. His smooth driving eased her motion sickness. She teased his car obsession, and after apologizing for her year-long silence over the soccer incident, they shared their first kiss. She ended the arrangement with the salaryman, desiring genuine emotional connection over transactional intimacy and fearing the call girl label. Agreeing to a final meeting for closure, Takumi saw her leave in the salaryman's Mercedes. He confronted her at school, accusing her of involvement with the Mercedes driver and demanding distance, leaving her shocked at his discovery. After weeks of estrangement, Natsuki insisted they remain friends despite not dating. Meeting at Lake Akina, she clarified she terminated the arrangement. When Takumi claimed indifference, she argued his avoidance revealed his feelings of betrayal. She reiterated her apology and decision. During a Mount Akagi trip with Takumi and Tsukamoto, Natsuki suffered severe motion sickness. Alone, she accidentally scraped a parked car with her watch, provoking a confrontation with the owner's girlfriend. Later, when the same couple passed them, she urged Takumi to race and defeat them, restoring her self-esteem. His victory thrilled her, feeling like a rollercoaster. Natsuki planned to attend Tokyo university after graduation, noting her parents were less strict than Shiraishi's, who opposed similar plans.