NiziU announced Monday that it will release Sour Grapes, its first Korean mini album, on September 28 at 6 p.m. The announcement came through a prologue film the group posted to social media at midnight.

This marks NiziU's first Korean release in about 18 months, following the single "LOVE LINE" in March 2025. The prologue film centers on grapes as its main visual, showing members encountering the fruit across different scenes before shifting to a darker, more surreal aesthetic. JYP Entertainment says the concept hints at temptation, desire, and curiosity, though the agency has not yet shared the track list or revealed which song will be the lead single.

NiziU made its official Korean debut in October 2023 with the single album Press Play. Both "HEARTRIS" from that release and "LOVE LINE" topped Korean music program charts.

While building anticipation for Sour Grapes, the group has remained active in Japan throughout 2026. NiziU's second Japanese EP, GOOD GIRL BUT NOT FOR YOU (Good Girl But Not for You), reached number one on Oricon's weekly and combined album rankings. The group's first Japanese best album, Portfolio, earned a Gold Disc certification from the Recording Industry Association of Japan.

NiziU also completed an arena tour across five regions in Japan this year and held its second dome tour, NiziU Live with U 2026 'NiziU : THE CINEMA.'

With Sour Grapes, NiziU returns to the Korean market after the success of its Japanese releases, signaling the group's continued momentum across both territories.