Yoo Yong Ha

On August 31, 2017, Youha, known as Yoo Yong ha, performed the pre-debut song Hug Me of the team of trainee tentatively named in OUIBOYS along Sihun, Kangwoo, 1BELL, and Yoon Myung. On October 25, 2018, Yoo Yong Ha was introduced as a contestant of Under Nineteen with his moving poster. The poster revealed that he was a part of the rap team.

He finished in sixth place, thus becoming a member of the project group 1THE9. On April 13, 2019, the group officially debuted with the mini album XIX. 1THE9 officially disbanded on August 8, 2020, following the release of their final mini album Good Bye 1THE9.