Hina Kusunose is a high school student and tennis club member whose athletic participation is frequently interrupted by injuries. These recurring accidents stem directly from her pronounced clumsiness, causing her to trip or bump into objects.

Her path crosses with Yuuta Morisaki when she collides with him in a school hallway, sparking immediate romantic feelings. Unbeknownst to Yuuta at first, they share a history as childhood friends connected through his late mother. Hina vividly remembers a significant promise made with Yuuta during that time, while he recalls neither her nor their agreement.

Hina's primary motivation centers on attending the Ocean Festival with Yuuta to view fireworks together, driven by a local belief that couples doing so will find lasting happiness. This goal becomes complicated when she observes Yuuta interacting with other girls, leading her to mistakenly assume he is romantically involved elsewhere. These misinterpretations breed significant emotional distress, intensifying her anxiety and insecurity.

Personality-wise, Hina exhibits sensitivity and naivete, often internalizing worries about Yuuta's perceived disinterest. She copes by confiding in her friend Youko and engaging in self-talk with a green plush crocodile toy for comfort. Despite setbacks, she demonstrates persistent dedication to expressing her feelings to Yuuta.

Across the narrative, Hina gradually overcomes jealousy and hesitation. She eventually confesses her feelings to Yuuta during the Ocean Festival, leading to mutual acknowledgment of their bond. This prompts Yuuta to recall their childhood promise – a commitment to reunite and watch fireworks together – fulfilling her emotional journey.