Yasuna Ajimu is a high school student who recently relocated from Tokyo to a coastal town months before the main events. She has long blond hair, often styled with distinctive antenna-like strands reaching her waist, and green eyes, typically seen in her sailor school uniform.

She continues to process the significant loss of her former boyfriend, Yuuma Otomine. This unresolved grief impacts her emotional availability, complicating new relationships as lingering feelings for Yuuma remain a persistent internal struggle.

Academically, Yasuna shows interest in history and the Japanese language. Music is central to her identity; she actively composes and performs her own songs, specializing in Hawaiian music played on the ukulele. She performs twice weekly at a local establishment called J.O.D., receiving positive audience reception.

Her first encounter with Hirosuke Nakaido occurs during their commute at a train station. Accidental contact from his tennis racket handle leads her to mistakenly perceive him as a molester, and she misinterprets his subsequent attempts at apology as stalking, forming an early negative impression.

After mutual friends clarify the misunderstanding, Yasuna's relationship with Hirosuke shifts from antagonism to friendship. However, her capacity for romance remains complicated by her attachment to her deceased boyfriend. Gradual development occurs as she begins to acknowledge deeper, non-platonic feelings toward Hirosuke, signaling potential emotional growth.

Her familial connections include her mother, Tamaki Ajimu. School associates include peers Suzue Takemoto and Kazuki Izumiya.