Monkey D. Luffy and his Straw Hat pirate crew have survived the East Blue. With a bounty on Luffy’s head and a ship under their feet, they now set their sights on the ultimate goal: the legendary treasure known as the One Piece. But to find it, they must first conquer the most dangerous stretch of ocean in the world. Their destination is the Grand Line, a lawless ribbon of sea where compasses fail and the laws of nature bend.

As One Piece: Into the Grand Line begins, the crew makes their final preparations in Loguetown, the town of the beginning and the end. It is here that the Pirate King, Gold Roger, was executed, inspiring the Great Pirate Era. But the Marines are waiting. The ruthless Captain Smoker, a man who commands the power of smoke itself, has his eyes set on the rookie who dares to follow in Roger’s footsteps. A narrow escape launches Luffy, Zoro, Nami, Usopp, and Sanji toward the impossible wall of Reverse Mountain, their gateway to the Grand Line.

The new world immediately proves hostile. The crew is swallowed whole by a massive whale named Laboon, a creature mourning a long-lost crew. Inside, they meet Crocus, the eccentric keeper of the lighthouse, who teaches them how to navigate the Grand Line using Log Pose needles. The journey then takes them to Whiskey Peak, a town that welcomes pirates with feasts and music. It is a trap. The entire town is a lair for Baroque Works, a powerful criminal syndicate of bounty hunters. While Luffy enjoys the party, Zoro single-handedly dismantles the town’s defenses, only to find the crew entangled with a mysterious ally: the rebel princess Nefertari Vivi, operating under the codename Miss Wednesday. Vivi reveals that Baroque Works is sowing chaos in her homeland, the desert kingdom of Alabasta, and she must return to stop them. Luffy, angered by the syndicate’s cruelty, agrees to take her home, making the Straw Hats the number one target of the organization’s mysterious leader, the Warlord of the Sea known as Sir Crocodile.

Chased by the Baroque Works agents Mr. 5 and Miss Valentine, the crew sails for the prehistoric island of Little Garden. Here, time has stood still for a hundred years. Two giant warriors, Dorry and Brogy, continue an ancient honor duel. Luffy befriends the giants, but Baroque Works intervenes again. The crafty Mr. 3, who can manipulate wax with his Devil Fruit powers, traps the crew in a deadly diorama. To survive, Usopp must find courage he never knew he had, and the crew learns of an even greater threat: the officer agent known as Miss All Sunday, who seems to know more about their future than they do.

Disaster strikes when Nami falls gravely ill. The only hope is to find a doctor on Drum Island, a winter nation ruled by a tyrant who murdered the previous king. The island’s only physician is the eccentric Dr. Kureha, a 140-year-old woman living in a castle atop a mountain. Climbing the mountain in a blizzard nearly kills Luffy and Sanji, but they reach the doctor just in time. Here, they discover Dr. Kureha’s assistant: Tony Tony Chopper. Chopper is a reindeer who ate the Human-Human Fruit, giving him the ability to think, talk, and transform. An outcast rejected by both humans and animals, Chopper dreams of becoming a great doctor like his father figure, the late Dr. Hiriluk. As the tyrant king Wapol returns to reclaim his castle, Luffy defends Chopper’s home. In gratitude, and in pursuit of his dream, Chopper unfurls his pink hat and joins the Straw Hats as their ship’s doctor.

The season concludes with the crew setting sail for Alabasta. They carry a desperate princess, a shape-shifting reindeer, and the full wrath of a Warlord aimed at their backs. The Grand Line has tested their bodies and their bonds, but the true fight for the fate of a kingdom is only just beginning. With the enigmatic Miss All Sunday watching from the shadows and the sinister Mr. 0 pulling the strings, the Straw Hats sail toward a conflict that will define them as a crew.