On the survival competition show Peak Time, Heejae and Ireah participated as two members under their former group name Masc (Korean: 마스크; stylized in all caps).

[1] After finishing in second place, it was announced on May 3, 2023 that they had signed an exclusive contract with PCS Entertainment and would embark on their new start and reform the group as a duo.

[2] Masc officially debuted as a four-member group comprising Heejae, Woosoo, 26, and ACE under JJ Holic Media on August 19, 2016.

[4] Ireah joined the group as a new member along with Moonbong, Doeun, and Chibin, and they were introduced with the release of Masc's third single, "Do It", on October 12.

[12][13] In February 2023, members Heejae and Ireah first appeared as a singing duo on the JTBC reality competition show Peak Time.