TV Special
Description
Chiyoko Wato serves as the primary companion to Hosuke Sharaku, her full name referencing Sherlock Holmes' assistant John Watson. She attends the same school as Sharaku and exhibits a tomboyish personality, often using the male pronoun "boku" for herself. She demonstrates self-confidence and occasionally resorts to physical aggression when provoked. Her background identifies her as the daughter of a local Shinto priest.

Chiyoko forms a complex relationship with Sharaku, acting as his best friend, protector, and occasional love interest. She becomes one of the few aware of his transformation when the cross-shaped bandage covering his third eye is removed, revealing his malicious alternate personality and extraordinary psychic abilities. Her role involves managing the consequences of these transformations. She sometimes removes the bandage herself to leverage Sharaku's intelligence and powers during crises, but actively works to replace it before he can execute plans for world domination, positioning her as a crucial counterbalance to his destructive capabilities. Her fascination with Sharaku's true nature persists despite recognizing the danger he poses.

She participates in global adventures alongside Sharaku, investigating ancient ruins and mysteries tied to the three-eyed civilization in locations including Arizona, Easter Island, and Mexico. During these expeditions, she provides practical assistance while attempting to mitigate the fallout from Sharaku's actions. In the Black Jack animated series, an alternate portrayal reimagines her as Sharaku's older sister. In this continuity, she adopts a more conventional supervisory role, frequently reminding him to complete homework and display greater self-confidence, with Sharaku's bandage remaining intact without transformation.

Her character development progresses from initial episodic encounters to involvement in longer narrative arcs concerning Sharaku's origins. She maintains consistent traits throughout these stories, including physical strength, quick thinking, and dedication to counteracting Sharaku's ambitions when his third eye is exposed.