Chaesol, Jeewon (formerly known as Jiwon), Ye Ah (formerly known as Haeun), Sunn (formerly known as Viva), and Belle (formerly known as Lucky) were debuted on August 30, 2017, as members of C9 Entertainment first girl group Good Day.

[3] In October 2017, Members Chaesol, Jeewon, Sunn, and Belle had competed in KBS2 reality television series The Unit.

[6] Subsequently, from November 12 to 17, the remaining members were introduced in the order: Semi, Chaesol, Sunn, Belle, Ye Ah, and Seline.

[22] On April 27, 2021, J9 Entertainment announced that Ye Ah and Sunn had left the group and terminated their contracts with the agency due to undisclosed reasons.

[30][31] Member Belle was not involved in this comeback due to her participation in SBS survival show Universe Ticket under her real name "Jin Hyeon-ju".

[32] On January 17, during the finale of Universe Ticket, Belle secured her spot as a member of the debuting group, Unis.

[37] On December 3, C9 Entertainment announced through the Cignature fan cafe that the group has disbanded after unanimously agreeing to end their activities on November 30, 2024.