The sea in our world has been polluted. All sort of trash have been thrown into the sea, making it unpleasant to live underwater. One of the inhabitants of the sea, Ika Musume (Squid Girl) seeks to exact revenge on humanity for throwing trash into the sea. Clueless about the surface, she tries to invade humanity alone and rule over the world, only to find herself slaving away at one of the nearest beach houses for breaking a side of its wall.