Natsuki Mogi attends high school with Takumi Fujiwara. Outwardly friendly and cheerful, she formed a close bond with Takumi during their senior year, reconnecting after an earlier fallout caused when he punched her then-boyfriend for boasting about their relationship. While projecting an innocent image to classmates and holding a part-time job, Mogi secretly participated in compensated dating with an older salaryman. This arrangement evolved from paid companionship to sex. Unaware he was the father of her friend Shiraishi, her secret life became a source of conflict when Takumi witnessed her leaving the salaryman's Mercedes and distanced himself. Mogi repeatedly sought reconciliation, explaining she ended the arrangement because she fell in love and desired a genuine connection over transactions. Despite her efforts, their relationship remained strained. Seeking independence from her parents, she later moved to Tokyo for university, ceasing direct involvement in Takumi's life. In the recap "New Initial D the Movie Battle Digest," Mogi appears only in archival footage; no new developments specific to her occur. Her narrative concludes with her departure to Tokyo, while Takumi pursued racing and eventually married another woman.