Fena: Pirate Princess (Japanese: 海賊王女, Hepburn: Kaizoku Ōjo) is a Japanese anime television series created and produced by Production I.G. A co-production between Crunchyroll and Adult Swim, the series aired on the latter's Toonami programming block from August to October 2021. A Japanese broadcast followed from October to December 2021. The story follows Fena Houtman, who seeks to unravel the mysteries of her family’s past and a legendary treasure tied to the name "Eden".

Ten years after surviving a brutal attack on her family’s ship, Fena Houtman washes ashore on the colonized island of Shangri-La. In the present, desperate to escape the island, Fena sells her virginity and enters an arranged marriage with Maxiver Jr., a volatile British soldier. Her escape plan falters, but she is saved by Otto and Salman, former knights of her family, and a group of hidden warriors, including a samurai whose familiar eyes hint at Yukimaru’s identity. He knocks her out to ensure her safety as they flee from British soldiers and town guards. Fena, Otto, Salman, and a stray dog named Brule escape Shangri-La on a raft, landing on Goblin Island, home to a Japanese community led by Sanada Yukihisa. Sanada, whose ancestor was saved by the Houtmans, gives Fena a mysterious clear stone from her father, tied to his final voyage and the word "Eden". After cutting her hair and meeting the warriors who aided her escape, Fena receives a ship and Sanada’s elite Goblin Knights to pursue the stone’s secrets. Meanwhile, Royal Navy officer Abel hires pirate Grace O’Malley to hunt Fena.

Fena’s crew, aboard the submersible Bonito II, stops at Bar-Baral for supplies. There, Fena, with warrior twins Kaede and Enju, uncovers a lead on another clear stone from Idar-Oberstein, Germany. Maxiver Jr., now leading pirates under Abel’s command, ambushes them. Yukimaru, revealed as the samurai, is wounded protecting Fena, and Maxiver is captured, later facing execution by Abel’s orders. As the Bonito II sails to Germany, Fena struggles to learn combat. In Idar-Oberstein, the Burgomaster reveals the stone’s French origin, linked to Joan of Arc’s nickname, La Pucelle d’Orléans, with a purchase date of 1436—five years after her execution—deepening the mystery. Sailing to Orléans, Fena’s crew explores a buried temple, where she experiences visions guiding them through catacombs to a glowing altar. O’Malley’s crew, the Rumble Rose, ambushes them, demanding "coordinates to El Dorado" etched in Roman numerals on the stone. O’Malley kidnaps Fena, trapping the Goblin Knights in the catacombs. The Goblin Knights escape using gunpowder, but O’Malley delivers Fena to Abel on his ship, the Blue Giant. Abel, obsessed with a painting of Fena’s mother, Helena, claims the Goblin Knights are using Fena to find Eden, where the legendary Kusanagi Sword is hidden. Yukimaru defies orders to rescue Fena alone, while O’Malley attacks the Blue Giant in revenge after Abel refuses payment. Abel destroys O’Malley’s ship with a powerful cannon, triggering Fena’s memories of her family’s ship attack, orchestrated by the British. Yukimaru, wounded again by Abel, is saved by the Goblin Knights, who escape with Fena to Chaouen for medical aid.

In Chaouen, Goblin Knight Shitan blames Fena for Yukimaru’s injuries, but they reconcile. Yukimaru recovers and vows to protect Fena, kissing her hand in a tender moment. Abel, haunted by memories of Helena - burned at the stake for eloping with Franz, Fena’s father - pursues Fena to fulfill Helena’s wish to reunite in Eden. Fena’s childhood song, "Vice Versa", combined with the stone’s numerals, reveals coordinates to an uncharted island. There, the crew discovers a treasure-filled cave and a "lattice stage" where Fena’s dance unlocks Eden’s true entrance. As Abel and the Royal Navy invade, a chaotic battle erupts. Abel, delusional, sees Fena and Yukimaru as Helena and Franz, and wounds Yukimaru before collapsing. An entity, the Observer, reveals Fena as the "Maiden of Choosing", tasked with deciding whether to preserve or reset the world, losing her memories either way. Fena chooses, and the island collapses. Yukimaru awakens on a beach, finding an amnesiac Fena with altered appearance. The Goblin Knights, carrying salvaged treasure, resolve to retrace Fena’s journey to restore her memories. Yukimaru’s confession of love sparks a partial memory recovery, suggesting he holds the key to her past.

The Samurai Seven (サムライセブン, Samuraisebun) are a group of elite samurai that resides on Goblin Island, and Fena as her loyal pirate crew. They are the descendants of the Goblin Knights that decimated 3,000 Spanish soldiers at the Battle of Dunkirk and were "feared as the incarnation of Lucifer himself".

The Rumble Rose (ランブルローズ, Ranbururōzu) is a band of pirates led by O'Malley who are partially responsible for the attack on the ship ten years ago that led to the death of Fena's father. They also allied with Abel to partly obtain Fena for him and partly to get the coordinates to El Dorado. Each of its high-ranking female members have names similar to the famous female pirates and/or Navy members in history.

A branch of the British Empire's military and is one of the factions after Fena ever since they were partially responsible for the attack on the ship ten years ago that led to the death of Fena's father. Among its known personnel are:

The series was directed by Kazuto Nakazawa, Tetsuya Takahashi, and Saki Fujii. Asako Kuboyama penned the series' scripts, while Yuki Kajiura composed the music. The opening theme song is "Umi to Shinju" (海と真珠; lit. "The Sea and a Pearl") performed by Junna, while the ending theme song is "Saihate" (サイハテ; lit. "The Farthest Shore") performed by Minori Suzuki.