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.
(Source: Aniplex of America)