A new two-part animated special, Lego One Piece, is framed as a story told by Usopp, the Straw Hat Pirates' resident sharpshooter and self-proclaimed liar. Shortly after the reindeer doctor Tony Tony Chopper joins the crew on the winter island of Drum, Usopp decides to welcome him by recounting their previous voyages. True to his nature, Usopp does not simply remember events; he rebuilds them as exaggerated heroic tales from the perspective of a builder, turning their past struggles into a grand, embellished narrative.

The story within the story follows the rubber-bodied captain Monkey D. Luffy, whose limbs stretch like rubber after eating a mystical Gum-Gum Fruit, as he gathers his eclectic crew. His first mate is the three-sword-wielding bounty hunter Roronoa Zoro, who dreams of becoming the world's greatest swordsman. They are joined by the skilled but money-obsessed navigator Nami, who longs to map the entire world, and the kicking chef Sanji, who seeks the legendary sea All Blue where all the oceans meet. Usopp himself is part of the crew, a kind but insecure sniper who aspires to be a brave warrior of the sea.

The action ranges from the relatively calm East Blue to the treacherous waters of the Grand Line. Early conflicts include a showdown with the sawshark fish-man pirate Arlong, who terrorized Nami's home village, and encounters with other flamboyant villains such as the limb-severing Buggy the Clown. As Usopp narrates, these dramatic moments from the live-action adaptation's first two seasons are recontextualized with the signature physical comedy and brick-based action of Lego animation, turning sword fights, sea battles, and dramatic escapes into a playful, highly unreliable retelling. The special focuses on the crew's formative adventures as they set sail on their first ship, the Going Merry, with the ultimate goal of finding the legendary treasure, the One Piece.