Hina Setoguchi is a first-year student at Sakuragaoka High School and the younger sister of Yuu Setoguchi. Her family lives next door to the Enomoto family, which has made her childhood friends with both Natsuki and Kotaro Enomoto. She has a petite stature, standing 149 centimeters tall, and is recognized as the shortest member of her peer group. Hina has light pink hair that she usually wears in two low pigtails that reach her neck, though she sometimes wears it down to her shoulders. Her eyes are purple, and her standard school attire is often supplemented with a yellow cardigan during colder weather or a short-sleeved white shirt when it is warm. At home, she prefers casual clothing, such as a striped hoodie and shorts, and will occasionally pin her bangs back.

Her personality is bubbly, energetic, and expressive, and she tends to show her emotions in an exaggerated manner whether she is happy or upset. Despite this cheerful exterior, Hina harbors deep-seated insecurities, particularly regarding her struggle to fully convey her romantic feelings to her crushes, which causes her significant frustration. She is perceptive and empathetic, allowing her to form strong friendships easily, as demonstrated when she helps Arisa Takamizawa come out of her shell. Hina also has a tendency to befriend those who are marginalized, shown by her early kindness to Koyuki Ayase before he gained wider social acceptance. She is perceptive enough to quickly discern the romantic feelings of others, even recognizing Kotaro's affection for her before she fully acknowledges her own. Hina is doted on by her brother Yuu, a relationship that has made her somewhat spoiled. She freely borrows his clothes and plays his video games, and despite occasional disagreements, she deeply admires him as a kind and mature ideal figure.

Hina's role in the story is primarily as a protagonist following her own romantic journey. Her first love began in middle school with an upperclassman named Koyuki Ayase. This crush was sparked by an awkward and embarrassing encounter in which he accidentally saw her underwear, an incident that paradoxically led her to become captivated by his warm smile. She nurtured these feelings for years and resolved to confess after following him to Sakuragaoka High School. However, her plans were complicated when Koyuki, who harbored feelings for Natsuki Enomoto, graduated. In her second year, Hina wrote him a love letter but witnessed him distraught after overhearing a confession between Natsuki and Yuu. When she finally shouted her own feelings, Koyuki misinterpreted her confession as an act of pity and rejected her. At her lowest point, Kotaro Enomoto intervened, walking her home and inviting her to his soccer tryouts. This moment marked a turning point in her life. She began regularly supporting Kotaro at his soccer events, and through their frequent and sometimes contentious interactions, she came to appreciate his steadfastness. She gradually came to recognize Kotaro as her hero, and her romantic feelings shifted from Koyuki to him. Their relationship eventually culminates in mutual love, with Kotaro confessing openly and Hina responding affectionately.

In terms of her key relationships, Hina shares a sisterly bond with Natsuki Enomoto, with whom she often plays platformer video games. She is close friends with Arisa Takamizawa, who plays a significant role in helping Hina realize her own feelings for Koyuki and later supports Kotaro from behind the scenes. Her circle of friends also includes classmates like Ken Shibasaki and Kodai Yamamoto. Hina is a member of the Track and Field club, where she participates as a hurdler and acts as a mentor to a junior named Hiyori Suzumi. Outside of school, her hobbies include playing video games.