Rain Boy manifests as a ghostly boy accompanied by perpetual rainfall, always clutching a ragged umbrella regardless of weather. Appearing lonely, he exhibits a fascination with human possessions, especially rain boots. His supernatural ability allows him to control rainfall, which he employs to grant wishes for those who befriend him.

Originating in a rural mountain area, Rain Boy first met the human boy Mota under a bridge during a storm. Desperate to obtain Mota's rain boots, Rain Boy offered three wishes in exchange. This pact defined their relationship. Demonstrating a gentle and patient nature, Rain Boy honored the agreement by granting Mota's wishes—including extinguishing a devastating fire threatening Mota's home—even after Mota eventually forgot their pact.

Following the third wish that stopped the fire, Rain Boy waited faithfully under the bridge for Mota to deliver the boots. Unaware, Mota moved away and grew into adulthood while Rain Boy continued waiting for decades, showing unwavering loyalty to their agreement. Rain Boy's existence remained fixed at their meeting place, showing no signs of aging or altered appearance.

Forty years later, an elderly Mota remembered his childhood promise and returned to the bridge. Rain Boy was still present, having waited the entire time. Mota finally gave his rain boots to Rain Boy, fulfilling the long-delayed agreement and resolving Rain Boy's lingering attachment to the human world.

Rain Boy embodies themes of patience and the weight of promises, functioning as a symbolic figure. His background as a spirit and motivations beyond the rain boots exchange remain undefined within the narrative.