"One Piece: The Curse of the Sacred Sword" is the fourth animated feature film in the "One Piece" franchise, released in 2004. The story centers around the Straw Hat Pirates as they arrive on Asuka Island, a place known for its prison and the legendary sword Shichiseiken. The sword is said to grant immense power but is cursed, bringing calamity to those who wield it. The crew becomes entangled in the island's turmoil when Zoro, the crew's swordsman, is accused of a crime he did not commit and is imprisoned.

The island's warden, Gasparde, a former Marine officer turned criminal, seeks to harness the power of Shichiseiken for his own ambitions. Gasparde manipulates events to frame Zoro, using the chaos to further his plans. Meanwhile, the Straw Hat Pirates, led by Monkey D. Luffy, work to clear Zoro's name and uncover the truth behind the cursed sword. The crew faces numerous challenges, including battles with Gasparde's forces and the island's prison guards, as they strive to protect their friend and prevent the sword's curse from causing further destruction.

Key characters include Luffy, whose determination drives the crew forward; Zoro, whose loyalty and strength are tested; and Nami, Usopp, Sanji, and Chopper, who each contribute to the crew's efforts in their unique ways. The film explores themes of loyalty, justice, and the consequences of unchecked ambition, as the Straw Hat Pirates confront both external enemies and the moral dilemmas posed by the cursed sword. The narrative builds to a climactic battle, where the crew must unite to overcome Gasparde and the sword's curse, ensuring the safety of the island and its inhabitants.