Hanabi Ayase is a twelve-year-old sixth-grade student with brown eyes and brown hair usually worn in twin pigtails. Her physical development compared to peers causes her personal concern. She exhibits a child-like, innocent personality marked by strong empathy and intuition. A firm sense of justice drives her to defend classmates facing bullying. Hanabi maintains a close-knit circle of friends, chiefly Yui Aoi and Marin Ogura. While her kind, inclusive nature makes her popular with female classmates, she also experiences bullying from some peers.

Her romantic relationship starts with Yuuto Takao, the most popular boy in class. Paired for a music assignment requiring flute duets with neighbors, they practice on the rooftop. There, Hanabi accidentally witnesses teachers kissing, stumbles backward, and is caught by Yuuto, resulting in their first kiss. This sparks mutual feelings, and they begin dating. Their relationship faces challenges from Cocoa Hamana, who actively pursues Yuuto and undermines Hanabi through mean-spirited actions.

Her childhood friend since kindergarten, Ayumu Tsutsumi, re-enters her life after returning from Tokyo. Though Ayumu harbors long-standing romantic feelings for her, he initially masks them with coldness, earning the nickname "Emperor" and causing Hanabi apprehension. His jealousy of her relationship with Yuuto manifests in attempts to sabotage it, like deliberately making her miss a date. Ayumu eventually confesses openly. Hanabi, while shocked, intends a respectful rejection. This escalates into a competition where Yuuto and Ayumu agree to a race, the winner earning the right to be with her.

Throughout these experiences, Hanabi navigates first love, complex social dynamics, and personal insecurities. She evolves from initial shyness and reluctance to express her feelings toward greater emotional awareness and assertiveness in relationships. Her journey involves learning about communication, honesty, and the complications of early adolescent romantic attachments.