Hatsune serves as a young attendant at the Yukishiro brothel, the residence of protagonist Takashiro Shuugo. Orphaned since early childhood with no living relatives, she has lived at Yukishiro for most of her life.

Physically, Hatsune stands 135 cm tall and weighs 28 kg, possessing a slim build, pale skin, and brown eyes. Her short brown hair features a bob cut with blunt bangs, typically adorned with a ribbon accessory. She wears a kimono.

Despite her fragile appearance, years of working alongside adults at the brothel have cultivated a levelheaded, kind, obedient, and proactive personality, embodying traditional "Yamato Nadeshiko" virtues. Her daily routine involves cleaning and reading.

Hatsune forms a strong attachment to Shuugo, serving him diligently by bringing meals and attending to his needs morning and night. Shuugo taught her to write during their time together, and she becomes defensive if anyone speaks ill of him. Within the narrative, she represents one potential romantic path for Shuugo; in her specific resolution, he abandons his investigation into the central mystery to remain with her, leaving the case unresolved.

Following Yukishiro's closure, former madam Ujaku takes Hatsune in, granting her the surname Amemiya. She subsequently works as a waitress at Cafe Moon World, continuing her diligent work ethic while training in cooking.