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"SURPRISE" is produced by KZ, Jeon Da Woon, and Crazy Melody with the rap lyrics written by member Inhaeng. Monday Kiz' Lim Han Byul also participated in the chorus.

Their agency stated, "'SURPRISE" is a romantic song which describes a pure-hearted guy who is willing to give up everything for the one he loves and plans a surprise party to confess his love."

Their repackaged 2nd single special music card album 'SURPRISE' consists of title track "SURPRISE" and all of the songs from their previous 2nd single album 'Hello HALO'.