"Riki-Oh" is a Japanese manga series created by Masahiko Takajo and illustrated by Toshio Maeda. It follows the story of Riki-Oh, a martial artist who is wrongfully imprisoned and must fight his way through brutal opponents in a violent prison environment. The series is known for its graphic violence and intense action sequences. The manga was adapted into a live-action film in 1991, which gained a cult following for its over-the-top fight scenes and unique blend of horror and comedy. "Riki-Oh" has influenced various media and is often referenced in discussions about extreme martial arts and cult cinema.