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One day a girl who lives on a southern island dropped her precious anklet in the ocean. A boy picked it up who has magical power. It is a warm and nostalgic story of a friendship between them depicted through an anklet in the beautiful and harsh ocean.
The crew of the Harukaze relax after midterm exams, and a Coco receives a new mission.
Protagonist Gunzo Chihaya and his friends, with the help of renegade Fog A.Is, head towards the United States to present blueprints for a weapon that will turn the tides of war in humanity's favour. It is easier said than done because Gunzo and the rest of Arpeggio's crew have gotten the attention of the mysterious Admirality Code. Now they must face a new Fleet of Fog threat known as “Fog Student Council,” who are mental models dressed like high school girls. The Fog Student Council preaches that Earth's morals must correspond to the Fog's morals.
Akeno Misaki and Moeka China share one goal—to join the Blue Mermaids! A group of fierce women, the Blue Mermaids are key to keeping peace among the seas and coastal cities in this age of maritime trade. To be a part of this elite group of sea protectors, they must succeed at Yokosuka's Marine High School. Akeno and Moeka, together with their classmates, will take the plunge to become Mermaids!