Natsuki Mogi is a high school student who becomes the love interest of Takumi Fujiwara during the events of the second stage. She is first introduced as a customer of Takumi’s tofu delivery service, showing an early interest in him that develops into a romantic relationship. Her appearance is that of a teenage girl with short brown hair and brown eyes, and she is one of the few characters who is not intimidated by Takumi’s extreme driving style.

Her background includes a hidden and troubled secret: she has been involved in compensated dating, known in Japanese as enjo kousai, with a much older man who drives a white Mercedes. She refers to this man as “Papa.” This arrangement began before she met Takumi and continues into the second stage, even after she has shared a kiss with Takumi. During the second stage, she attempts to end this relationship but is caught by Takumi, which creates a major rift between them. Following this exposure, she decides to leave her past behind and works a part-time job to support herself honestly.

Personality-wise, Natsuki is initially portrayed as sweet, reserved, and kind, but she also carries a deep sense of insecurity and a strong desire for acceptance and love. She is sensitive to the emotions of those around her and is naturally perceptive, able to read people’s feelings with ease. However, she struggles with opening up and maintaining a certain social image, which leads her to keep her secret life hidden. Her flaws—chiefly her involvement in compensated dating and her reluctance to be honest—make her a layered character who must confront her own mistakes.

Her role in the second stage is primarily emotional and dramatic. She serves as a catalyst for Takumi’s personal turmoil and his recklessness during his race against Kyoichi Sudou, as the revelation of her secret drives him to vent his anger in a dangerous and ill-advised battle. Her storyline highlights themes of trust, forgiveness, and the difficult process of change.

Natsuki’s key relationships include her bond with Takumi, which is tested severely by her secret. She also has a tense dynamic with her classmate Shiraishi, who, motivated by jealousy over Natsuki’s relationship with Takumi and resentment toward her own father (who is the same older man Natsuki dates), exposes Natsuki’s secret by leaving an anonymous note in Takumi’s shoe locker. Another important figure is the older man himself, whose presence represents the past Natsuki tries to escape.

Throughout the second stage, Natsuki undergoes significant development. She transitions from a seemingly ideal love interest to a flawed and troubled individual who must make difficult choices. By the end of this stage, she begins to take concrete steps to change her life—quitting the compensated dating, finding honest work, and trying to make amends with Takumi—though the damage to their relationship lingers.

Among her notable abilities is her lack of fear of Takumi’s racing, which sets her apart from nearly everyone else. She also has a talent for sensing others’ emotions, which allows her to connect with Takumi on a deeper level, even when he is otherwise distant. Her passion for cars and photography is mentioned, though these are secondary to her personal story.