Kuruku, also called Kukuruku or Kukurukku, began existence as a discarded puppet, mistreated by human owners. Cast adrift, he washed up at the edge of the world, a dumping ground for unwanted things. There, absorbing sunlight for 200-300 years granted him life and magic, forging a core of profound hatred for humanity.

He rules Nightmare Island, driven by vengeance for his abandonment and a desire to conquer loneliness. His goal is enslavement, transforming living creatures into "Living Puppets"—zombie-like beings resembling person-shaped wooden blocks. These puppets lose free will and individuality, becoming either building materials for his castle or magically controlled servants. He manipulates the young wizard Toby, promising magical knowledge to exploit Toby's wish to protect his sister Cheri from becoming a puppet like their parents.

Kuruku wields powers including shape-shifting into a floating rainbow orb or bubble, teleportation via light beams, and magic to animate objects or transform life. His typical form features a pointed face, crimson eyes, and red-orange hair beneath a red robe and magician's hat. His voice often carries layered distortion. He displays faux affability when pleased, but reveals cruelty and mania when opposed, openly savoring the fear he inspires.

His end comes when Unico and Cheri confront him. Severely wounded by Unico in a transformed state, Kuruku's physical form decays. Unico's offer of friendship drains Kuruku of the sustaining hatred that animated him. Deprived of this force, he reverts to an inanimate wooden puppet. Cheri later keeps this puppet form as a toy.