Natsuki Mogi, a high school student entangled in a romance with Takumi Fujiwara, begins as a sweet, reserved figure whose past complicates her present. A previous relationship with classmate Miki collapses after Takumi confronts Miki’s boasts about their intimacy. Seeking financial independence, she enters a compensated dating arrangement with a middle-aged salaryman—dubbed "Papa"—who drives a white Mercedes, a decision she later laments.

Her connection with Takumi strengthens through shared moments: trips to Lake Akina, beach outings, and unwavering support for his racing passion. Mutual confessions of affection and a tentative first kiss deepen their bond, though Takumi resists labeling their relationship. Tensions erupt when he uncovers her ties to the salaryman, driving them apart. She severs the arrangement, striving to mend trust, but their reconciliation remains fragile.

A harrowing encounter on Mount Akina sees Miki attempting to assault her, thwarted by Takumi’s snowy pursuit and rescue. Post-graduation, she resolves to attend university in Tokyo, seeking distance from her history. Inviting Takumi to join her, she faces his refusal as he commits to racing, culminating in a bittersweet farewell where love lingers but paths diverge.

The live-action film streamlines her arc, depicting her as an escort involved with the Mercedes driver. Takumi’s discovery sparks a confrontation, echoing the original’s unresolved separation.

Her journey navigates self-redemption amid societal pressures, shifting from concealed mistakes to candid accountability. Despite efforts to reconcile with Takumi, their futures unfold independently, marked by unresolved emotions and individual ambitions.