Riichi's life begins with his father Toshi winning money by betting on the gender of his child, and then naming him after a move in the game of Japanese Mahjong. As Riichi grows, even small victories in fights are followed by a family ritual: they get him drunk, and the next day he throws up in his classroom recorder. A turning point comes when Miss Itô visits their home and witnesses the pattern of abuse directed at Riichi's mother, a moment that casts a long shadow over the household. Toshi’s life outside the home expands into new indulgences as he begins an affair with a stripper named Akemi, deepening the strain within the family.
Riichi's world widens beyond his cramped home as his friend Kotetsu drags him into a broader, messy search for belonging. Kotetsu's grandmother wanders along the river in search of her paints, only to find the search in vain, and the disappointment is sealed by her eventual placement in a care home. Riichi and Gasu accompany Kotetsu on a perilous trip from Osaka toward his brother's place in Shikoku, driven by a shared hunger for something steadier, but money dwindles, and the journey ends with a painful return home to the same old cycle.
Back at school, Riichi becomes fixated on a new goal: to win the school’s first prize paints for Kotetsu's grandmother. The plan involves stealing supplies and constructing a life-size replica of the Apollo Lunar Module, a bold project that captures the imagination and tests the limits of their youth. The bold creation is met with violent resistance when Riichi's rival Sada and his gang smash it to pieces. Undeterred, Riichi and Kotetsu confront the rival crew and demand a rebuild, reclaiming their original ambition and driving the piece to completion. The finished model earns first prize, and the boys race to hand the paints to Kotetsu's grandmother, only to discover she has died at the riverbank where she sought color and meaning.
Societal pressure closes in as factories rise where old communal pillars once stood, and Riichi finds himself clashing with Sada again at a construction site that becomes a battleground. His father returns from protesting against the government, bringing with him the same complicated energy that has threaded Riichi’s life since the beginning. When Riichi comes home, he discovers his mother is gone, and the fear of abuse surges once more. The confrontation that follows is brutal, but it is tempered by the return of Riichi's mother and a fragile, ongoing invitation from [Toshi] to join him at cycling races, suggesting that the family’s story, painful as it is, continues to move forward in cycles that repeat and redefine the boundaries of love, loyalty, and resilience.
