Japan, 2019, just before the dawn of a new era. Suddenly, a rift to another dimension appears in the sky, revealing an alternative world "Shinkoku Nippon," with the sky and the earth upside down. This parallel world keeps their former militarism, with its era being Eternal Showa. The military invades the real Japan with giant humanoid robots called "Garann" and their gas weapons "Genmu", rendering our modern weapons ineffective. "Shinkoku Nippon" instantly seizes the government and achieves de facto conquest of Japan. The new era, "Reiwa," has not arrived for Japan.

Japan, 2019, just before the dawn of a new era. Suddenly, a rift to another dimension appears in the sky, revealing an alternative world "Shinkoku Nippon," with the sky and the earth upside down. This parallel world keeps their former militarism, with its era being Eternal Showa. The military invades the real Japan with giant humanoid robots called "Garann" and their gas weapons "Genmu", rendering our modern weapons ineffective. "Shinkoku Nippon" instantly seizes the government and achieves de facto conquest of Japan. The new era, "Reiwa," has not arrived for Japan.

To celebrate their graduation from university Kaori and her two friends visit Okinawa in southern Japan for a short vacation. At the vacation house, provided by Tadashi's uncle, a numbing stench awaits the girls, and can be traced to a horrendously deformed, legged fish that Kaori kills. More and more of these creatures appear and portend a horrific change for the animal life in the area. A phone call from Kaori's fiancé Tadashi in Tokyo quickly shows the scope of this epidemic, when he is also attacked by these mechanized fish. Kaori immediately sets out on an perilous voyage to find out what happened to Tadashi, helped by Shirakawa — a videographer in search of the truth behind all this...

The story centers on the growth and paths in life of Nikuko and Kikuko, a mother and daughter who lives on a boat.