One day, Kei, a young and struggling screenwriter, is surprised by an unexpected guest at her apartment door. The guest is Niko, a little girl and a secret child of the renowned actress Mifuyu Shibano. Kei is the only one who knows this secret, having worked for Mifuyu before she became famous. As Kei takes Niko into her home, she realizes that the child is very introverted. To connect with her, Kei initiates an exchange diary.