Fudō was raised within the Kamui ninja clan alongside the protagonist, enduring the clan's harsh and demanding training methods. A childhood sparring session resulted in a prominent facial scar, an event that ignited a deep-seated rivalry and lasting resentment toward the protagonist. Fudō's life took a dark turn after surviving the Fuuma clan's massacre of the Kamui. Abandoning the clan's remnants and its principles, he embraced a path of vengeance and the relentless pursuit of power, later becoming known as the "Black Kamui."

This chosen path transformed Fudō into a ruthless mercenary and assassin, operating solely for personal gain and the quest for ultimate strength. He mastered forbidden ninja arts, most notably the demonic Fudou Myouou technique. This dark power required the constant absorption of victims' life force to sustain itself, leading to physical transformations and an amplification of his aggression. His primary motivation crystallized into an obsessive pursuit of the Book of Ten, a legendary text believed to hold the ultimate secrets of ninja mastery. This obsession fueled direct and violent conflict with the protagonist, who also sought the book, thereby intensifying their personal rivalry.

Fudō actively hunted the protagonist, viewing his defeat as essential to proving his own superiority and achieving dominance. Their multiple confrontations across the story showcased Fudō's formidable wind-based ninjutsu alongside his dark Fudou Myouou powers. As the demonic energy increasingly consumed him, his physical changes grew more pronounced with each battle. The culmination of Fudō's character arc occurred in a final, decisive battle against the protagonist. Despite wielding immense dark power, Fudō was ultimately defeated. This final battle concluded with his death, an end that stopped his long descent into darkness and closed the chapter on the intense, long-standing rivalry between the two former clan members.