Nozomu, a middle school boy from Tokyo, arrives at his uncle’s house in a rural town in Kumamoto Prefecture for what he expects to be a quiet summer vacation. He is immediately confronted by his younger cousin Sou, a lively sixth grader with sun‑browned skin and no regard for personal space. Sou clings to Nozomu, sits on his lap, demands his attention, and teases him without any self‑consciousness. Nozomu, already harboring a painful incident from school back in Tokyo, finds himself both flustered and slowly drawn out of his shell by Sou’s relentless cheerfulness.

The story follows their daily life in the countryside—visits to the beach, exploring old sheds, festivals, and interactions with other relatives and local children, including the mischievous classmate Takeru and Nozomu’s own sister Aoi, a junior idol who drops in for a visit. Sou, though confident in her affection, does not fully understand her feelings as romantic; she simply believes Nozomu should be hers and acts on that impulse. Nozomu struggles to maintain his composure as her innocent yet intimate gestures grow more frequent.

A major turn occurs when Nozomu’s father, without consulting him, arranges for his transfer to a local school, extending his stay indefinitely. This revelation upsets Nozomu, but Sou tries to cheer him up, and he eventually accepts the new situation. As summer turns to autumn, Sou begins to feel romantic jealousy and confusion when other girls show interest in Nozomu, and she starts to mature emotionally. Meanwhile, Nozomu’s own trauma comes to light: he had been involved in a conflict at his previous school where his kind intentions backfired, leaving him isolated and scarred.

Subsequent arcs see the arrival of older cousins Tsumugi and Shiori, the development of a potential love triangle with a local girl named Mikoto, and the deepening of the bond between Nozomu and Sou. The story culminates in Nozomu being forced to return to Tokyo to confront his past directly. He leaves Sou behind, but the connection between them has grown too strong to be severed. The narrative is a blend of comedy, slice‑of‑life rural atmosphere, and earnest emotional growth, centered on two cousins navigating the blurred line between familial affection and romantic love.