"Happy Happy" is TWICE's 4th Japanese maxi single, released July 17, 2019 via Warner Music Japan. It comes in four versions: Limited Edition A (CD + DVD featuring the MV and MV making film), Limited Edition B (CD + DVD featuring the MV lip sync version and jacket shoot making film), Regular Edition (CD only), and the ONCE JAPAN fanclub edition. Limited Editions A and B and the Regular Edition each include 1 of 10 trading cards. The ONCE JAPAN fanclub edition is the standout collector version, containing an 8-page lyric booklet, 2 randomly selected trading cards from a 10-type set commemorating TWICE's 2nd Japanese debut anniversary, a 3×3 fold poster, and a benefits application serial code. The single carries 4 tracks: "Happy Happy," "The Best Thing I Ever Did (Japanese ver.)," a collapsedone remix of "Happy Happy," and an instrumental. The title track served as the CM song for Qoo's 20th anniversary campaign in Japan, and its accompanying dance making video was filmed in Hawaii. Its release was announced at the final date of the #Dreamday Dome Tour in Nagoya. The single earned RIAJ Platinum certification and later appeared on the &TWICE studio album. Exclusive single goods were sold at a release event at Intex Osaka on July 31, 2019, and online via the ONCE JAPAN shop through August 18.