The year is 2020, and it is off the coast of the Sea of Okhotsk. A "portal" suddenly appears on the bottom of the sea, leading to a different space-time. The unknown wilderness beyond it is called the "Demon World."
A group of dangerous protozoans, including the vicious crustaceans "Crab Soldiers," a major force in the Demon World, have rushed in to expand their territory into the human world! The United Nations set up a meeting to peacefully settle the situation, but all the envoys became their dinner. Modern weapons for humans were ineffective against the shell, which had a terrifying defensive power, and one by one, important bases of humanity fell . As fear and despair filled the world, only one person and one animal stood up. It was a girl of unknown origin, half human, half animal, "Eugene." And her guardian, "Johnny." For some reason, the claws she wields are filled with the power of the demon world, making it possible to easily crush the shells of the Crab Soldiers. Fighting poison with poison... there is no other way left. The future of humanity is entrusted to this cat-eared girl! Make up your mind!