"One Piece: Strong World Episode 0" serves as a prelude to the film "One Piece: Strong World," providing essential backstory and context for the main antagonist, Shiki the Golden Lion. The episode delves into Shiki's past, his rise to power, and his eventual imprisonment in Impel Down. A legendary pirate and former member of the Rocks Pirates, Shiki was once a rival to Gol D. Roger. After Roger's capture, Shiki launched a massive assault on Marineford, resulting in a fierce battle with Vice Admiral Garp and Admiral Sengoku. Despite his formidable strength, Shiki was defeated and imprisoned.

The narrative highlights Shiki's cunning and determination as he becomes the first person to escape Impel Down by cutting off his own legs to remove his seastone cuffs. Following his escape, Shiki disappears for two decades, secretly developing a plan to conquer the world using genetically engineered beasts. His ultimate goal is to destabilize the World Government and establish his dominance. The episode also introduces the Straw Hat Pirates, who are unaware of Shiki's return and his impending threat.

Key characters include Monkey D. Luffy, the captain of the Straw Hat Pirates, and his crew, who are central to the events of the main film. Shiki's backstory is intricately tied to the broader lore of the "One Piece" world, emphasizing his significance as a formidable adversary. The episode effectively sets the stage for the film, providing viewers with a deeper understanding of Shiki's motivations and the stakes involved in his grand scheme.