The story focuses on the past of Sawa Souda and Kyouko Yakumo when they were students together at Seishou Music Academy (Sawa being a third year, 74th class and Kyouko being a first year, 76th). It also introduces two new characters, Ichika Saegusa of the 74th class, and her seven year old sister, Chizuru Saegusa.

(Source: Shoujo☆Kageki Revue Starlight Wiki)