Anime
Detective Conan
Case Closed, known as Meitantei Conan is a Japanese detective manga series written and illustrated by Gosho Aoyama.
Jimmy Kudo is a high school detective who helps the police solve cases. During an investigation, he is attacked by Gin and Vodka who belong to a syndicate known as the Black Organisation. They force him to ingest an experimental poison called APTX 4869 to kill him without leaving evidence. A rare side-effect of the poison, however, transforms him into a child instead of killing him.
The ULTIMATE TRANSFORMATION
(Well, little Conan can see Ran naked without any problems anyway ^v^)