OVA
Description
Shunsaku Ban co-managed a shop in the United States with his friend Yushi. After witnessing Yushi's murder during a gang robbery, he assumed guardianship of Yushi's infant son, Sango. During their journey to Japan, Ban observed a flying saucer, immediately followed by the appearance of a mysterious green cat beside Sango. Sango and the cat then vanished during the voyage.

Years later, working as a private investigator, Ban discovered Sango had become an influential figure within the criminal underworld, manipulated by the green cat. He learned this cat was an extraterrestrial entity that attached itself to young individuals, fulfilling their desires while eroding their self-reliance and corrupting them. The cat, named Green by Sango, actively protected him and facilitated his criminal activities, including eliminating threats.

Ban dedicated himself to freeing Sango from the creature's influence. He tracked Sango to Monte Carlo, where Sango conducted high-stakes criminal operations under Green's guidance. Ban collaborated with a scientist studying the green cat phenomenon, acquiring a device designed to deprive the alien of carbon dioxide. Using this device caused Green significant distress, enabling Ban and authorities to intervene. Sango was arrested during the operation, though Green escaped.

In a final confrontation, Ban confronted Sango in a deserted house, urging him to kill Green to break free. He provided Sango with a gun. Green, hiding in the shadows, attempted to manipulate Sango into killing Ban instead. Sango resisted, prompting Green to reveal her grotesque true alien form. Ban then succeeded in killing the creature.

Across various media, Shunsaku Ban is consistently depicted as a middle-aged Japanese man with a portly build, bald head, and a prominent white mustache—though in "The Green Cat," he appeared younger and without the mustache during the initial events. His core traits include a strong sense of justice, paternal protectiveness, and a quick temper, often balanced by courage and determination in confronting threats. While frequently portrayed as a detective or teacher in other stories, his role here centered on his investigative efforts and unwavering commitment to rescuing Sango from alien manipulation.