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DSP Media tweeted, "? DSP Festival D-4? KARA-Rainbow putting the finishing touches on their practice! What are they preparing together? ;)!" The agency also added a behind-the-scenes photo of the 12 members channeling the cheerful and confident charms of one of the original girl groups, Fin.K.L. 

KARA and Rainbow will perform their label's former girl group Fin.K.L's hit song at the 'DSP Festival', which will be held at Jamsil Arena, Seoul on December 14 KST. Sechskies' Eun Ji Won, Jang Su Won, and Kim Jae Duk as well as Click B, SS501's Park Jung Min, and A-JAX will reunite with DSP Media for its first family concert in 22 years. 

Any guesses on which song they'll perform?