This is the R18 version which includes adult sex scenes!

This is the prequel to Showtime! Uta no Onee-san Datte Shitai 2

Fujimoto Shouji, a widowed single father who aspires to be a picture book author, encounters Takasaki Minami, a singing idol on the children's educational show O-nee-san to Uta-ou! (Let's Sing Along With Our Songstress!), outside work. As a television idol for children, Minami is lonely in her private life and is not allowed to fall in love. Any scandals are absolutely prohibited. Thus begins an adult love story with a songstress.