NiziU is bringing their first Korean mini album to listeners on September 28. The release, titled 'Sour Grapes', drops at 6 p.m. that day and marks a new chapter for the group in the Korean market.

The five-track album opens with the title track 'Sour Grapes', which reimagines Aesop's fable "The Fox and the Grapes" with a modern twist. The remaining tracks—'Petal's Song', 'emoji', 'Into The Dawn', and 'Lullaby'—weave together to create what the agency describes as a narrative flow similar to reading a musical fairy tale, with autumn themes running through the project.

In the lead-up to release, NiziU's label has been steadily rolling out teaser content across social media. A track video for 'Lullaby', released September 21, showcased dreamy visuals paired with a lyrical pop ballad melody, capturing a surreal atmosphere centered on the desire to stay close to a loved one. The song reflects the album's early autumn sentiment.

The visual concept teasers, built around a grape motif, reveal a notable shift in the group's presentation. Rather than their typical bright and approachable energy, the members display a more sophisticated aesthetic—described as kitschy and chic. A performance teaser for the title track hints at an intensified stage presence, suggesting the group will present a more mature version of themselves as the year progresses.

The release represents NiziU's first dedicated Korean-language mini album, positioning the project as a significant moment for their expansion in the Korean music industry.