"Breakthrough" is TWICE's 5th Japanese maxi single, released July 24, 2019 via Warner Music Japan — exactly one week after "Happy Happy," making the two a deliberate back-to-back summer double release. It comes in four versions: First Press Limited Edition A (CD + DVD + lyric booklet + 1/9 photocard), First Press Limited Edition B (CD + DVD + lyric booklet + 1/9 photocard), Standard Edition (CD + lyric booklet + 1/9 photocard), and a ONCE JAPAN fanclub edition. The DVD content differs between limited versions, with Edition A focusing on MV content and Edition B on making film footage. The single carries 4 tracks: "Breakthrough," "Fancy (Japanese ver.)," a taalthechoi remix of "Breakthrough," and an instrumental — making it the first physical home for the Japanese version of "Fancy." Billboard described the track as a dramatic, brassier electropop companion to "Happy Happy," designed to evoke the feeling of a cool summer night to contrast its counterpart's bright summer day concept. It was also used as the CM song for Japanese cosmetics brand Aube. The single earned RIAJ Platinum certification for physical shipments and later RIAJ Gold for streaming (50M+ streams, certified October 2025). A Korean version of "Breakthrough" was later included on the Feel Special mini album. Release event goods were sold at TWICE's "Twaii's Shop" pop-up stores.