Isamashii Chibi no Iinazuke

Nagato is an ordinary high school student, and Miku is an ordinary teacher except for her short height. They are childhood friends, and enjoy their life at the same school together with other classmates. But just before the summer holiday, Nagato is ordered to tidy up the school library with Miku. And that night, Gennosuke, Miku's grandfather, tells them that they are fiance and fiancee. They get totally confused to hear that. Their a little bit different summer holiday starts now....