G:amma

In January 2013, Junsu was introduced as a member of the boy group AlphaBAT. On October 21, Simtong Entertainment, in partnership with BOY London, revealed the members’ new stage names corresponding to the Greek alphabet, with Junsu adopting the stage name G:amma. He officially debuted as a member of AlphaBAT on November 12 with the digital single "AB City.

" Since 2023, with AlphaBAT on hiatus, he has pursued other activities, including acting, while focusing on his personal life.