Chitose Morinaga

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 had become every female student’s dream job.

The world's greatest blue sapphire, the "blue lapis fist", said to have sunk in a pirate ship in the late 19th century, on the coasts of Singapore. A local millionaire plots to retrieve it, and when it's exhibited in an exhibition at the Singaporean Marina Sands hotel, a murder takes place.