Mina Nagoshi attends a Tokyo high school alongside Asuka Mishima and Haruto Kirishima. Her significant introduction occurs when she invites Asuka to a school festival, only for Haruto to intervene by grabbing her hands and demanding she take him instead. While Haruto's true motive is contacting his ex-girlfriend at the school, Mina misreads his eagerness as romantic interest. This initial misunderstanding shapes her subsequent interactions and feelings toward him.

Deeply flattered by this perceived attention and moved by Haruto's tendency to evoke sympathy, Mina develops romantic feelings. She consistently misreads Haruto's words and actions to fit her belief in his affection, often leading to self-detrimental outcomes. Though she seemingly gives up after Haruto dates Asuka, an encounter during their college years reignites her interest. Learning of Haruto's breakup with Asuka and continuing to misinterpret his behavior, she becomes convinced he has loved her all along, fueling a resurgence of her romantic inclinations.

Mina possesses a girly yet hard-headed personality with distinct expectations about relationship norms. She knows what she wants but lacks accurate perception in social situations. Despite being on first-name terms with Asuka, they share minimal direct interaction or scenes.

Physically, Mina has orange hair and orange eyes. She stands 1.55 meters tall with measurements of 80-57-80. Her birthday is December 8, and her blood type is A.

Her narrative role centers on comedic misunderstandings stemming from her persistent misinterpretation of Haruto's intentions, embodying the "Butt-Monkey" trope through this pattern.