18+ Showtime! Uta no Oneesan datte Shitai

The story begins when Shouji Fujimoto, a widowed single father who aspires to be a picture book author, encounters Minami Takasaki, a singing idol on the children's educational show Oneesan to Utaou! (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.

(Source: ANN, edited)