On November 7, 2021, Leeseo was revealed as the sixth and final member of IVE. The group debuted on December 1, 2021 with the single album "Eleven".
2022: "Blue & Black"
On June 6, 2022, it was announced that members of IVE, OH MY GIRL, and CRAVITY would collaborate for a digital single that would be released as part of Starship Entertainment's ongoing collaboration project with Pepsi. That same day, the members of said groups that would be participating were revealed, including LeeSeo. The collaborative single, titled "Blue & Black", was released on June 28.