OH!!マイクロマン ～小さくなって女の子の色んなトコロに入っちゃお～

One morning, our protagonist, Maikuro Mitsuru, suddenly found himself shrunk to a very small size. Using that to his advantage, he started doing erotic things to various girls. Peeping the toilet and girls' skirts, sneaking into girls' clothes and underwear, entering the bathroom as he likes. Thinking everyday about new erotic ideas which can only be done because of his size, he started living a "fulfilling" life.