Gfriend's Eunha appeared in silver gold hair in the online showcase of GFriend's '回:Song of the Sirens'.

During the showcase, she revealed that she had the chance to work with producer Bang Si Hyuk (Hitman Bang), the founder of Big Hit Entertainment, on their title song "Apple". It was revealed that both Eunha and Yuju were able to participate in the production along with FRANTS, Pdogg, and Bang Si Hyuk.

Eunha revealed she was always interested in producing and writing songs but this was her first time taking part in producing a song, so she had some difficulties. However, producer Bang Si Hyuk helped her apply the melody and lyrics she wrote to their title song. She felt honored to work with producer Bang Si Hyuk and explained that she wants to work harder and put forth more effort.

Yuju also said in the interview that "there is a change in our image in this album concept, so I tried harder to interpret the song to express the song more, rather than just trying hard."

Meanwhile, GFriend's mini-album '回: Song of the Sirens' holds various songs of different genres and explains the story of a girl who contemplates as she is at crossroads about her future.

Their title song "Apple" is a trendy pop-song that uses a retro-trendy melody and the Vocal Chops technique which reminds the listeners of the song that sirens sing. Members Yuju and Eunha had participated in producing their title song, which makes the song even more meaningful to the group.