Shirasu Kinjou, born Isuke Fuuma, entered the world alongside his identical twin Isame within the Fuuma ninja clan. Both inherited the Kotarou Fuuma mantle as the clan's tenth-generation leaders during childhood. A traumatic rite of passage demanded by clan elders forced Shirasu to kill his own father, fracturing their family and causing their mother to withhold all smiles from him thereafter.

To conceal their survival and advance their quest to resurrect the serpent Orochi, the twins fabricated the Fuuma clan's extinction. When Kumo Taiko uncovered ties between the Fuuma and Orochi, Shirasu murdered him and inadvertently caused Kumo Koyuki’s death—parents to the Kumo brothers. Shirasu then infiltrated the Kumo household under the alias Shirasu Kinjou, a name bestowed by Tenka Kumo for his albino-like features after he refused to disclose his true identity.

For a decade, Shirasu served as the Kumo brothers’ housekeeper and caretaker at Cloud Shrine. He maintained a calm, polite facade while handling domestic tasks, though his cooking skills extended only to sweets. His white hair and purple eyes—distinctive Fuuma traits—occasionally aroused suspicion. Despite his original mission to locate Orochi’s vessel, he grew genuinely protective of Tenka, Soramaru, and Chutaro Kumo, threatening those who endangered them and acting as Tenka’s combat partner and confidant.

As Orochi’s resurrection neared, Shirasu betrayed the Kumos, exposing his identity as Kotarou Fuuma and his role in their parents' deaths. He furthered the Fuuma agenda by stabbing Botan, the brothers' supernatural ally. After Orochi’s defeat, consumed by guilt but bound to his clan, he attempted suicide by leaping from a cliff.

Surviving the fall, Shirasu returned to the Fuuma. Though resuming his ninja life, he carried enduring affection for the Kumo brothers, acknowledging that his time with them had softened him and revealed previously unknown warmth. He reflected on those years as "a warm, wonderful dream," a lasting imprint from his deception.