Originating from the OVA "Rain Boy" (Amefuri Kozō), adapted from Osamu Tezuka's manga, the character Rain Boy manifests as a diminutive ghost eternally shrouded in falling rain. His appearance features traditional Japanese wooden sandals (geta) and a tattered umbrella perpetually held overhead, with rain encircling him as an emblem of his spectral solitude.

While wandering the countryside, Rain Boy encounters a lonely human child and forges a bond. Intrigued by the boy's rain boots, he negotiates an exchange: three wishes granted in return for the footwear. The boy consents to this pact. Over time, the child matures and entirely forgets both the promise and Rain Boy's existence. Decades later, the adult man abruptly recalls his childhood vow. Spurred by this memory, he journeys back to his hometown, seeking the bridge of their initial meeting to honor his long-neglected pledge to the gentle ghost. The narrative explores memory, kindness, and the repercussions of abandoned commitments, depicting Rain Boy as a patient, spectral presence awaiting the fulfillment of their heartfelt agreement.