The dance-pop single "HAPPY 7 DAYS" was released by SME Records in 2015. The track features a synth-pop sound characteristic of the mid-2010s J-pop scene.
- The single was released on June 17, 2015.
- It was released by SME Records.
- The genre is dance-pop, synth-pop, and pop.
9nine is a Japanese pop group formed in 2005. They have released numerous singles and albums throughout their career.
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