"HAPPY HAPPY" is the fourth Japanese single released by TWICE. It was released in four versions: two limited CD+DVD editions (A & B), a regular CD edition, and a limited ONCE JAPAN fanclub CD edition. Limited editions A & B and the regular edition come with 1 of 10 trading cards and the ONCE JAPAN fanclub edition comes with an 8-page lyric booklet, a Japan debut 2nd anniversary commemorative trading card (2 random pieces of 10 types), a 3 × 3 fold poster, and a benefits application serial code. The title track was used as a CM song for Nippon Coca-Cola Qoo.
III. CD Tracklist
- HAPPY HAPPY
- The Best Thing I Ever Did -Japanese ver.-
- HAPPY HAPPY (collapsedone Remix)
- HAPPY HAPPY (Instrumental)
IIII. DVD Tracklist
IIIII. Limited Edition A
- "HAPPY HAPPY" Music Video
- "HAPPY HAPPY" Music Video Making Movie
IIIIII. Limited Edition B
- "HAPPY HAPPY" Music Video Lip Sync ver.
- Jacket Shooting - Behind the Scenes