Kanini is a minuscule anthropomorphized freshwater crab sibling dwelling with his family in a forest stream. He is the younger brother to Kanino, with parents Toto and Kaka. When Kaka departs upstream to give birth, Toto remains caring for Kanini and Kanino.

A fierce storm separates the family after Toto rescues Kanino from powerful currents; a sudden surge of bubbles propels Toto downstream, leaving the siblings vulnerable and alone. Confronting this crisis, Kanini shows resilience, joining Kanino on a perilous downstream quest to find their father. They must evade large predatory fish and navigate the dangers of their oversized, teetering world.

During the journey, Kanini displays emotional vulnerability, weeping over his father's apparent loss. Yet, he gradually cultivates courage and determination, actively helping overcome obstacles—like wielding their father's broken spear defensively against a fish. His actions prove vital for survival and their eventual reunion with the injured Toto, discovered in a cave. The successful rescue and Kaka's return with newborn siblings restore the family, underscoring Kanini's shift from dependence to an active role in protecting his kin.

The narrative highlights Kanini's growth into a "modest hero" through perseverance and confronting fears for his family's sake, despite his diminutive size and the overwhelming hazards of his environment.