Two years after the Summit War, Monkey D. Luffy plans to reunite with the Straw Hat Pirates in the Sabaody Archipelago. However, the Marines obstruct Luffy's path with overwhelming force. Meanwhile, the Straw Hats must also foil the schemes of a group of impersonators acting in their likenesses. With two years of intensive training with allies old and new, Luffy regroups with his friends aboard the Thousand Sunny to set sail for the New World. As the Straw Hat Crew departs for Fish-Man Island, new threats creep up from the abyss. But more determined than ever to become the King of the Pirates, Luffy is prepared to defeat any enemy that may stand between him and his dream.

After an accident sent her family to their deaths in the ocean, Hinako Yaotose keeps returning to the thought of sinking forever into the sea herself. With Miko Yashiro as her only friend, Hinako manages to keep up a semi-happy facade, but whenever Miko leaves her side, she slips into despair. Everything changes one summer when she meets a mysterious girl with eyes as deep and clear as the sea, drawing Hinako in like nothing else has in a long time. During her absent-minded search for the girl, Hinako is suddenly pulled underwater by a beastly deep-sea creature, only to awaken to the presence of the girl—Shiori Oumi—who takes on a monstrous form and kills Hinako's attacker. Despite this heroic act, Shiori's intentions are no different from any other monster's: she wants to eat Hinako. The following morning, Shiori walks into Hinako's class as a transfer student, and Hinako cannot help but smile—at last, someone who could fulfill her quiet wish for death has appeared before her.

Marin and her younger sister Urin are seafolk who happen upon something quite strange: a beautiful silver ring lost beneath the waves. The kind-hearted Marin, intent on returning it to its owner, drags a reluctant Urin along with her to the sky world despite reminders of a turtle elder who left for the surface and never returned. After locating the ring's owner, Kanon Miyamori, they learn that Kanon had tossed it into the sea after her boyfriend dumped her earlier that day. Though Marin insists that such a lovely item should not be thrown away, Kanon discards it once again. As they search for the ring, Urin becomes separated from the other two and accidently breaks the seal on a stone coffin, releasing an evil being known as Sedna. Sensing Sedna's release, the formerly missing turtle elder, Matsumoto, reveals himself to Kanon and her companions, naming Marin as the Priestess of the Sea. Together with the Priestess of the Sky, she has the power to seal Sedna away again. And as luck would have it, during an encounter with one of Sedna's minions, Kanon discovers that she is the Priestess of the Sky. Though Kanon is hesitant, she and Marin decide to work together to save the world from the evil that threatens it.

Despite recently turning 17, the otherwise ordinary Yucie still has the body of a child. Having stopped growing past the age of 10, Yucie yearns to fully mature into an adult body. One day, she is chosen as a candidate for the title of Platinum Princess, given once in a thousand years to whoever is worthy of the Eternal Tiara—a mysterious crown said to grant any wish. She's not alone either, as four other candidates also compete to have their own wishes granted by the crown. As a result, Yucie enrolls at the nearby Princess Academy in order to grow her heart and work towards becoming qualified for the Eternal Tiara. With her family, rivals, and even the principal of the academy there to lend a hand, will Yucie's much-desired wish finally come true?