Ojisan to Marshmallow: Hige-san to Yume Mashmallow Episode 1

Habahiro Hige awakens at his desk at work, but much to his surprise, he has become a baby! To make things stranger, Iori Wakabayashi walks in wearing a school uniform but doesn't recognize him as the baby. Upon being picked up and held by her, Hige discovers that he doesn't just have the body of a baby but the mind of one as well. [Written by MAL Rewrite]