From MangaUpdates:

On her way to her first day of high school, Renge Ohyama meets a weird girl who appears to be a life-sized doll. But she isn't some advanced mechanical creation or even a magical doll. No. A scary looking middle age man controls her movements, puppet-like, and speaks for her via ventriloquism. Unfortunately, this perverted-seeming old man and his doll happen to attend her new school. Even worse, is in the same class and sits right behind her. And it seems the doll wants to be friends...