Shinryaku! Fushigi Kenkyuu-bu

The sea in our world has been polluted. All sorts of trash were thrown into it, making it unpleasant deep down in the sea. 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 seeks to invade humanity alone, trying to rule over the world... only to find herself enslaved by one of the nearest beach-houses for breaking one side of the wall! (Source: Hidoi)

The "girls comedy" series follows a protagonist named Daisuke who cannot decide on a club to join because he does not have anything he particularly wants to do. He has an encounter that changes his school life.