Sunny Days originally debuted as a five-membered group in 2012, being introduced as "vocal-idols". The girls had undergone rigorous training for about two years, and boasted excellent singing skills. They were even invited to perform live for an event in China before their domestic debut.

Their debut song was titled "Take Away", written by Kim Doo-hyun, a composer known for creating hits for A Pink, Girls Day, and Abavenue. "Take Away" featured a bluesy piano sound mixed with trendy, electronica-style string instruments. The members also were able to show off their beautiful vocal harmonies.

Come 2013, Sunny Days decided to add two more members: Bi-cheon and Gyu-hee. Bi-cheon was the former winner of "K-Pop World Festival", having competed as a Chinese competitor. She can speak four languages total: her native Chinese tongue plus Korea, English, and French.
Gyu-hee can also speak multiple languages: Chinese, Korean, and English.