Sanzou is a human who awoke from a 1000-year cold sleep destined to prevent global destruction. His mission requires collecting 49 legendary keys to unlock the Tokyo Metropolitan Government building, called the Twin Headed Dragon Door, crucial for stopping the spread of the Destruction Virus infecting robots known as asobots. Guided by a prophecy warning of the world's end within one year if the keys remained uncollected, he initiated this quest.

He wields a magical harmonica capable of influencing asobots. Initially ineffective against virus-infected units, he used it to heal non-infected asobots or enhance their attacks, notably empowering the protagonist Goku. After securing six keys, the harmonica transformed in appearance and gained the power to heal even virus-infected asobots. Early on, Sanzou cursed Goku, rendering him physically weak against women and children, claiming the curse would lift only upon reaching their final destination; it was removed near the quest's conclusion.

Sanzou is the son of Kuzo Genjo and the former lover of Rhea, recognized as the progenitor of all asobots. He observed physical and behavioral similarities between Rhea and the asobot Meeyon (also spelled Miyon), noting Rhea's essence manifested more strongly in Goku. Throughout the journey, he acted as a protective older brother figure to Suzie, a human companion who joined the group after her father's death.

In the final arc, Sanzou confronted the primary antagonist Ryutaro Demon, also known as Professor D., his father's rival who sought the keys for destruction. He battled alongside Goku, Yazu, and other allies. After collecting all 49 keys and curing asobots afflicted by the Destruction Virus, he chose to travel back in time with the group. This decision followed the discovery of a feather linked to Professor D. entering a temporal wormhole leading to the past. Sanzou concluded their journey with the statement: "The real treasure is none other than the treasure of the journey."