Mika

In March 2018, Mika (then known by her real name Yu Dahyun) was revealed as a member of Polaris Entertainment's trainee team Polaris Junior. However, the trainee team became inactive soon after in April 2018. Sometime in June 2018, Mika (then known by her real name Yu Dahyun) was revealed as one of four members of the pre-debut girl group Root Sixteen.

However, a few months later, their debut was cancelled and all of Root Sixteen's SNS accounts were deleted. On December 21, 2023, Mika was revealed as a member of the upcoming girl group Geenius. They debuted on January 5, 2024 with the single album "Voyage".