Hanabi Natsuno, a high school student, returns to her hometown after six years away, seeking a fresh start. She moves into the Tachibanakan female dormitory, where her experiences rapidly grow emotionally charged and complex. Her personality features a pronounced tendency to become easily flustered, frequently blushing and exhibiting visible embarrassment in unexpected or intimate situations with other residents. She demonstrates a kind and expressive nature, showing concern for others' well-being, such as recommending a bath to Konomi Fujiwara to prevent her catching a cold after finding her by the river.

Her background includes a childhood connection to the area, specifically sharing a "secret place" by the river with Konomi. There, they caught freshwater crabs, played house, and collected rocks. Initially, Hanabi struggles to recognize Konomi after their long separation, citing Konomi's grown-up appearance. This shared history forms the foundation of their renewed relationship.

Central to her story is entanglement in emotional dynamics with Iori Takamura and Konomi Fujiwara. Upon first encountering Iori, Hanabi experiences intense admiration, describing Iori's "pure beauty," silver hair, snow-white skin, and specific physical attributes, leading to immediate fascination and recurring thoughts about Iori's identity. This fascination evolves into active attempts to understand Iori, including spying and feeling depressed when unable to decipher her behavior. Moments like Iori asking if Hanabi likes her, offering to sleep together, or attempting physical closeness frequently trigger Hanabi's intense shyness and confusion. Concurrently, her relationship with Konomi deepens through experiences like hiding from wild boars during an observation trip, recalling a celebratory kiss, and planned activities like bathing together. Apologizing to Konomi for not realizing how much Konomi valued Hanabi's childhood promise to always be there signifies a key moment of emotional clarity.

Her development involves navigating physical and emotional intimacy within the dormitory. She experiences repeated situations involving nudity or near-intimacy, such as accidentally falling into Konomi's bathtub, witnessing Iori undressing, hiding in a closet with Iori leading to unintended physical contact, or encountering Sonoa Mitsui while feverish. Events like a water gun survival game removing clothing or a ping pong game involving underwear removal consistently provoke shock and embarrassment. Despite this, she gradually exhibits proactive emotional connection, like dragging Iori by hand to watch Tanabata Summer Festival fireworks before pulling away flustered, or resolving to create fun memories with Iori upon learning she lacks special ones. Her decision to resolve issues with her aunt to remain at Tachibanakan and her commitment to Konomi—holding hands and settling on being together until high school graduation—mark significant points of resolution.