Cinderella Boy (Japanese: シンデレラボーイ, Hepburn: Shinderera Bōi) is a one-shot manga created by Monkey Punch. It was originally published in the Kobunsha magazine Popcorn in 1980. An alternate version was published in Anime DO in 1982. The plot follows the adventures of impoverished private detective Ranma Hinamatsuri and his thrill-seeking rich girl partner Rella "Cindy" Shirayuki in a futuristic city named "Kirin Town". Kirin Town is a lawless European city-state with its own currency with the name of the city being a pun on the English word for "killing". The two are badly injured when they stumble across an organised crime operation and are put back together into the same body by a mysterious doctor. Every night the stroke of midnight, their shared body changes both form and identity. Ranma becomes Rella, or vice versa. Neither is aware of any actions or situations their partner is involved in, completely losing consciousness until twenty-four hours later, when the change comes around to them again.

The names of the story's protagonists both reflect the nature of their change.

Discotek Media have licensed the anime for a North American release.