CSR (첫사랑/Cheos-Sarang, formerly known as 05class) is a 7-member girl group under POPMUSIC and RBW Entertainment Japan. The girl group's concept is a class of young girls who were born in 2005. The group consists of: Sua, Sihyeon, Yuna, Seoyeon, Duna, Geumhee, and Yeham. They debuted on July 27, 2022 with the mini album “Sequence: 7272“. They made their Japanese debut on July 3, 2024 with the mini album “L'heure Bleue“.