Side-B : Memoirs of Echo Unseen

"Side-B: Memoirs of Echo Unseen" (stylized as "side-B: memoirs of echo unseen") is the first single album by Billlie. It was released on October 23, 2023 with "Dang. (Hocus Pocus)" serving as the single's title track. "BYOB (Bring Your Own Best Friend)" was pre-released on September 27, 2023. The physical album comes in two versions: Blue and Violet. Members Suhyeon and Moon Sua were unable to participate in recording and promotions of this album due to them being on hiatus due to health reasons.

1. 1.DANG! (hocus pocus)
2. 2.BYOB (bring your own best friend)
3. 3.DANG! (hocus pocus) (English Ver.)
4. 4.BYOB (bring your own best friend) (English Ver.)