The Equinox is a triathlon racer from Trek, a company that has won many races, including the Tour de France, with its superior technology in carbon materials. It is an all-rounder with excellent aero performance, excellent stability at high speeds, and a ride and performance similar to the company's general road racers.

The story is set in Tokyo, where an old school right in between the neighborhoods of Akihabara, Kanda and Jinbocho is in danger of consolidation and closure. Nine girls, centering Honoka Kosaka, have stepped up to defy the imminent danger facing their school. “If we want to protect our beloved school, we need to do what we can? we need to become idols!” Hoping against hope there’s something they can do about this, the girls strive to become famous, spread the word about their school, attract more students, and save the day. Now their “School Idol Project” begins to make their dreams come true! “Make our dreams come true!”

A third-year student at Otonokizaka Academy. She is the student body president of Otonokizaka Academy and a dance coach for μ's. She was raised in Russia, the home of ballet, where she received a gifted education in ballet from an early age, and although she had great hopes for her future as a ballerina, she failed in her career. Her dancing ability is at a professional level. At first, Eri was skeptical of Honoka Kousaka's plan to increase the number of applicants to Otonokizaka Gakuin and prevent the consolidation of Otonokizaka Gakuin through publicity for the school idol program, but Honoka's enthusiasm inspired her to join μ's herself. Her grandmother is Russian, and she is fluent in Russian. Her habit is to say "Harasho" in Russian.