Sango Yuno is the son of Yuno, who co-managed a dry cleaning shop with Ban Shunsaku in the United States. After gangsters kill Yuno during a shop attack, Shunsaku takes responsibility for the infant Sango and returns to Japan with him. During their journey, a flying saucer appears overhead, and a green cat materializes in their vehicle’s backseat. Sango forms an instant attachment to the cat, naming it Green despite Shunsaku’s objections. Both vanish mysteriously during the voyage.

Years later, Sango resurfaces as an adult under Green’s influence. The cat, an alien entity, fulfills Sango’s desires while eroding his self-reliance and manipulating him into crime. Shielded by Green, Sango gains power in the criminal underworld. Green isolates him from Shunsaku, now a detective investigating the green cat phenomenon, and enables Sango to subdue foes and evade consequences, deepening his dependence. Sango promises Green he will expand his criminal territory to preserve their bond, complying with her directives.

Shunsaku tracks Sango to Monte Carlo, where Sango exploits Green’s wish-granting for profit. Using a device designed by a scientist studying the green cats, Shunsaku disrupts Green’s environment, distressing her. Police arrest Sango during the confrontation while Green flees. Later, Shunsaku leads Sango to a deserted house, urging him to kill Green to break her control and supplying a gun. In the basement, Green tries to manipulate Sango into killing Shunsaku. Sango refuses, unable to commit the act. His defiance triggers Green to reveal her monstrous alien form. Her death severs the parasitic bond, ending Sango’s manipulated existence.