Aikatsu Stars! — Episode 21

Aikatsu Stars! features the protagonist Yume Nijino. Yume aims to become a top idol, and she enrolls in the Yotsuboshi Gakuen. This academy has a special group called the S4, who are the top four active idols in the school. Yume and the other first-year students aim to become a part of the S4. (Source: Anime News Network, edited)