The story of Showtime! ~Uta no O-nee-san Datte Shitai~ begins when Shōji 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 O-nee-san to Uta-ou!, 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.