One morning, our protagonist's, Maikuro Mitsuru, suddenly found himself being shrank to a very small size. Using that to the advantage, he started doing erotic things to various girls.

Peeping the toilet and girls' skirts, sneaking into girls' clothes and underwears, entering the bathroom as he like.

Thinking everyday about new erotic ideas which can only be done because of his size , he started living a "fulfilling" life.