Fudou, raised within the Kamui ninja clan alongside the protagonist, endured the clan's harsh training methods. A childhood sparring session resulted in a prominent facial scar, igniting a deep-seated rivalry and resentment towards the protagonist. Surviving the Fuuma clan's massacre of the Kamui plunged Fudou into darkness. Abandoning the clan's remnants and principles, he embraced vengeance and the pursuit of power, becoming known as the "Black Kamui."

This path transformed Fudou into a ruthless mercenary and assassin, operating solely for personal gain and the quest for ultimate strength. He mastered forbidden ninja arts, notably the demonic "Fudou Myouou" technique. This dark power required constant absorption of victims' life force to sustain itself, physically transforming Fudou and amplifying his aggression.

His primary motivation crystallized into an obsessive pursuit of "The Book of Ten," a legendary text believed to hold ultimate ninja secrets. This obsession fueled direct and violent conflict with the protagonist, who also sought the book, intensifying their personal rivalry. Fudou actively hunted the protagonist, viewing his defeat as essential to proving superiority and achieving dominance. Their multiple confrontations showcased Fudou's formidable wind-based ninjutsu alongside the dark Fudou Myouou powers, with his physical changes growing more pronounced as demonic energy consumed him.

The culmination of Fudou's arc occurred in a final, decisive battle against the protagonist. Despite wielding immense dark power, Fudou was ultimately defeated. This battle concluded with Fudou's death, ending his descent into darkness and the long-standing rivalry.