Narumi Kato is a young Japanese man who trained in Kung-Fu under Liang Jian-Feng in China. He suffers from Zonapha Syndrome, requiring him to provoke laughter from others to avoid respiratory failure and intense pain. Lacking comedic skill, his attempt to survive as a clown often frightened people. His appearance includes a muscular build, shoulder-length black hair that later turns silver, sharp brown eyes that also become silver, a pointy nose, and fair skin. An explosion cost him his left arm, replaced first by a bionic puppet arm resembling Harlequin's, with further prosthetics added by fellow Shirogane during later battles.

Narumi perceives himself as selfish but possesses an underlying kindness, readily helping those in need and confronting injustice. He fiercely opposes those who harm children or devalue life, leading to conflicts with some Shirogane. Zonapha attacks create urgent, sometimes desperate, attempts to elicit laughter, especially during perilous situations.

He utilizes Chi-Kong martial arts: Dragon's Grip (grabbing an arm, striking the face, kicking the leg), Hard Chi-Kong (focusing vital energy to withstand powerful attacks), and Crushing Fist (channeling Chi into a straight punch). Treatment with Aqua Vitae granted him accelerated healing, increased resistance, longevity, and eventual immunity to Zonapha Syndrome, transforming his hair and eyes silver and marking him as a Shirogane warrior fighting Automatons.

His story begins distributing circus flyers in a bear costume when he encounters Masaru Saiga, a boy targeted by kidnappers. During a Zonapha attack, Masaru's laughter saves Narumi, forging a bond. Narumi rescues Masaru from assailants revealed as Automaton puppets. He allies with Masaru's silver-haired protector, Shirogane, though their partnership starts with arguments and clashes. Together, they protect Masaru from familial inheritance plots and Automaton threats.

Narumi travels to the Sahara with allies, including his master's daughter and the original Shirogane Lucille, to unite global Shirogane against the Automaton-spread Zonapha epidemic. Severe battle injuries, faint episodes, and further limb loss lead to prosthetics provided by comrades Tor, Timbavati, and Rockenfield. An explosion causes amnesia, stranding him in an American medical facility housing Zonapha-afflicted orphans. There, he uncovers dark truths about the syndrome's catatonic effects and the "Midnight Circus," a group spreading the disease.

His journey reveals his identity as the modern reincarnation of Bai Yin, an alchemist linked to the origins of the Automatons. This connection deepens his role in confronting the centuries-old conflict involving Aqua Vitae and the Soft Stone.