In July 2011 After School was divided into two sub-groups, A.S. BLUE and A.S. RED. Both groups released a single and promoted their own songs at the same time. While A.S. RED features a sexy concept, A.S. BLUE features a cute and fresh concept. Both groups' debut singles were released as the main group After School's 4th single.
- [2011.07.20] BLUE