Monkichi, a male monkey with sleek black fur and piercing golden eyes, is adopted by Robin amid the unfolding narrative. He forges a deep bond with Monmi, a fellow monkey, and their partnership proves vital in aiding the protagonists during critical junctures. Monkichi wields a mystical flute bestowed upon him, capable of commanding other monkeys, a device crucial for orchestrating their coordinated efforts in battle.

In the climactic showdown, the flute’s power allows him to merge an army of monkeys into a colossal samurai monkey entity. This towering figure then merges with a swirling bat swarm, forming a monolithic hybrid entity pivotal in combating the primary antagonist’s mechanized forces. Monkichi’s contributions underscore his alliance with the protagonists, anchored by his loyalty to Robin and the tactical deployment of his flute’s unique abilities.