Ayuru Ohashi

Kazuma Hoshino moves to the beautiful countryside to take care of his little brother, Ayumu Hoshino. They ended up they getting lost on their way to the Japanese Inn.

Living by the sea, protecting the sea, and journeying across the sea... They're the Blue Mermaids! Because of a shift in tectonic plates around 100 years ago, Japan lost much of its area to submergence. To preserve Japan's territories, coastal cities sprung up, one after the other. Eventually, they became marine cities, and along with the expansion of sea-lanes to connect them, the need arose for a sizable staff to protect the seas. At the same time, maritime jobs were becoming more popular among women. Hence, the Blue Mermaids, tasked with keeping the seas safe, had become every female student's dream job. This is when childhood friends Akeno Misaki and Moeka China enroll in a marine high school in Yokosuka, along with other girls who share their goal of becoming a Blue Mermaid.

In this world, Sensha-do (戦車道), the art of tank-combat, is a traditional Japanese martial art for girls. Miho, a girl who just transferred into the Ōrai Girls' Academy in Ibaraki Prefecture, has been ordered by the academy's student council chairperson to join the school team and compete in the national Sensha-do championships.

Otonokizaka High School is planning to close within three years. However, nine female students come together with one thing in mind—form a pop idol group to revive the school’s popularity and keep it from shutting down. 'In order to protect our beloved school, there’s only one thing we can do...become pop stars!'