UNI was announced on the VOCALOID EMPIRE fan-cafe on November 9, 2014. The announcement stated that YAMAHA portrayed a positive position on UNI's development, which would commence so long as there are no "huge unforeseen consequences", and that SBS A&T was to provide assistance for UNI's voicebank development. Demo songs for UNI would be selected from the most popular original songs uploaded to VOCALOID EMPIRE.
The announcement also stated that Korean VOCALOID development "may not end with UNI only".
Dr. Yun, a Korean producer and admin of VOCALOID EMPIRE, revealed in the comment section that ST MEDiA planned to record UNI's voicebank with a professional voice actress who would be chosen before the end of November. He also confirmed that UNI's design concept was finalized and that they were only considering a Korean voicebank for the time being.
On November 29, the staff stated that they were looking for voice provider suggestions. Fans could comment the voice provider they think would suit UNI and the staff would check periodically to see the most recommended choices. They would keep the most popular suggestions in mind.
On December 7, one of UNI's full designs was revealed at the Shanghai Exhibition Center in China. However, if fans did not agree with the design or if the design received backlash, editing or changing the design was in consideration. The design that was revealed was a finalized design, but was not the finished product. It was stated that the design on the banner was also not final and they wanted to showcase the hairstyle which would be kept. In terms of the voice provider, they were looking for someone who would have a calm, warm, and mature-sounding voice. 
Around the end of April 2015, fans asked questions about UNI's development to the staff of ST MEDiA. The company answered that they could not reveal whether UNI would be put on the VOCALOID3 or VOCALOID4 engine, nor the voice provider, at this point in time. They were still hoping for a 2015 release and confirmed that overseas fans would be able to purchase her.
On July 11, when asked about if UNI was on the VOCALOID3 engine, VOCALOID EMPIRE confirmed that UNI was in production for the VOCALOID4 engine since the beginning.
On July 27, several questions were brought up to VOCALOID EMPIRE's twitter account. UNI would have more than one voicebank and it was hinted that she may be able to sing in multiple languages. It was also noted that she may not meet the estimated summer 2015 release.
Her design was originally intended to be revealed on August 15, but was announced early on August 4 due to the silhouette receiving 300 likes on Facebook. VOCALOID EMPIRE said they wanted to produce banks in Chinese and/or English, but that UNI would most likely be released with 2 in total. However, the certainty of these claims was later thrown into question by a translator. Korean tweets suggested UNI would be released with one voicebank, but more if she was successful. On September 8, it was revealed that UNI would not be released until 2016.
On June 17, 2016, a sample of UNI's voicebank was released. It was revealed that she would be capable of cross-synthesis and was set for release in September. An English voicebank was slated for 2017. It was also mentioned that her voice provider had changed during production. At this point in time, the demo utilized a "Soft version" and was still in development.
On November 16, it was later announced that UNI's Korean voicebank was delayed to January 2017. However, her Append voicebanks, Power and Soft, would be released separate from the original voicebank in Summer 2017.
On January 25, 2017, ST MEDiA acknowledged UNI's delay and said that they were not able to release her in January due to the wait for YAMAHA's final approval. ST MEDiA hoped that UNI would be released by February and that she would not be delayed further. It was also announced that ST MEDiA opened up their own online store: Character Planet. UNI's voicebank would be sold on Character Planet on its own or as a starter pack with the VOCALOID4 editor.
On her official product page, it was noted that UNI's pre-order sale would last from February 2 to February 12. Her release date was set for February 14.
|어제, 오늘, 내일 (Eoje, Oneul, Naeil)||YouTube|
|작별 카운트다운 (Jakbyeol Countdown)||YouTube|
|愛情販売機 (Aijou Hanbaiki)||YouTube|
|Trial/Demo Vers?: No Starter Available?: Yes|
|UNI is a Korean female vocal.|
|Phonetic notes as noted:|