In Episode 12, Mizuhara states she would sing a Song from the Bands the Peggies or Halca at Karaoke. The Peggies & Halca are the bands that Performed the Opening & Ending Themes of the Anime, Respectively.
Based on a Japanese manga series written and illustrated by Reiji Miyajima. It has been serialized in Kodansha's Weekly Shounen Magazine since July 2017.