Kaori Yamasaki is a high school student and member of her school's track and field club. She possesses practical skills like welding, learned in home economics. Her father chairs Yamasaki Construction, which once faced severe financial strain. During this crisis, Kaori overheard her parents discussing unavoidable layoffs, though her father expressed reluctance, concerned for his employees' well-being.

To aid her family's business, Kaori strategically befriended Aya Chiyono, whose father held political influence. This connection contributed to reviving Yamasaki Construction, leading to increased contracts and public speculation about their newfound success. Kaori confided in peers about the difficulty of maintaining the friendship, finding it exhausting and comparing herself to "Cinderella" beside a "princess." Despite these calculated origins, their bond deepened into a genuine and close friendship, with Aya becoming Kaori's best friend.

Kaori developed romantic feelings for Aya but suppressed them due to fear and anxiety, unable to express her emotions. During a week-long stay at the abandoned Satomi coal mine to celebrate Aya's birthday before her move, Kaori and her friends encountered immigration authorities targeting Malet, an undocumented resident. After repelling the authorities, Masahiko Honda exposed the students' secrets online, including Kaori's initial motives for befriending Aya.

Reading the online exposure of her past intentions caused Kaori significant distress, making her cry. Later, when Aya confessed her own romantic feelings to Kaori, their mutual affection became clear. Kaori reflected on the difficulty of carrying her unspoken emotions throughout their friendship, acknowledging a persistent desire to confess that was hindered by fear.