[3] The group was composed of nine members: Euijin, Feeldog, Daewon, Marco, Ko Ho-jung, Ji Han-sol, Jun, Chan, and Kijung.

Ji Hansol is a former SM Rookies trainee who left the company in 2017 to sign with J-FLO Entertainment and debuted with Newkidd.

In July 2017, KBS announced their new survival show that would create male and female unit groups, with nine members each, among idols who had already debuted.

On February 21, 2018, it was revealed that the male group, Uni+ B, would hold their first fan-meeting on March 3 at Blue Square iMarket Hall.

[7] On February 24's broadcast of The Unit's Special Show, the final nine male contestants that formed "Uni+ B" became UNB following the announcement.

[11] Later, on June 18, conceptual photos were released, which revealed the identities of the faces in the poster:[12] All except for Jueun had participated on The Unit alongside UNB.