Billlie (Korean: 빌리), previously known as Mystic Rookies, is a seven-member girl group under MYSTIC Story. The group consists of the following members: Moon Sua, Suhyeon, Haram, Tsuki, Sheon, Siyoon, and Haruna.

They debuted on November 10, 2021, with the mini-album The Billage of Perception: Chapter One. Additionally, they celebrated their Japanese debut on May 17, 2023, with the Japanese version of their hit song “GingaMingaYo (the strange world)”.