Toubei Kirigakure, a ninja master and father to Kotaro and Kasumi, calls Aozora City home. He diligently trains his son Kotaro in ninjutsu, though Kotaro consistently dodges these lessons. During one training session, a mishandled explosive damages a shrine seal imprisoning the demon king Gokuark, accidentally freeing the demon world servant Yaminorius III.

Confronting Yaminorius III early on, Toubei attempts direct combat. The sorcerer punishes this interference by cursing him, transforming Toubei into a dog. Unaware of his true identity, his family adopts him as a pet, naming him Gonzales (Gon). Despite his canine form, Toubei retains his human intellect and ninja expertise. He constructs a secret training chamber beneath his doghouse, using this hidden space to mentor the Ganbar Team—Kotaro, Rikiya, and Yousuke—while concealing their identities and his own from the world.

Toubei spends most of the series trapped as a dog, gradually adopting canine behaviors like burying bones and digging. He wrestles with these instincts but persists as the team's advisor. When Kotaro is temporarily absent, Toubei disguises himself as "Shinobi Ganbar" to pilot Ganbaruger and defeat a demonic threat, safeguarding the team's mission. He regains his human form only for the final battle against the Three Great Demons, aiding the Ganbar Team directly to secure victory.

Following the conflict, Toubei resumes his human life without further supernatural incidents. His relationship with Kotaro remains marked by paternal concern and continued ninja training, persistently strained by Kotaro's rebelliousness.