On October 25, 2018, Khael was introduced as a contestant of Under Nineteen under his birth name, Lee Sangmin, with his moving poster. The poster revealed that he was a part of the rap team. He was part of the top 19, but was eliminated in the final episode.
2021: Debut with MIRAE
On February 7, 2021, he was introduced as the sixth member of MIRAE. His profile film was released later that day. On March 17, he officially debuted with the group's first mini album Killa.