One Piece Manga Chapter 21

Responding to a distress call, Luffy, Zoro, and Sanji land on an island and discover that Ain has de-aged everyone, including them and Law (into a baby), into children. They and other child characters, including Sabo and Smoker, defeat Ain and a giant robot. When everyone returns to their original age, Law wakes up naked, causing a comical scene.