
On August 16, it was announced that their third EP The Billage of Perception: Chapter Two, featuring lead single " Ring Ma Bell (What a Wonderful World)", would be released on August 31. On August 8, 2022, it was announced the group would be releasing a direct sequel to their first EP. On March 1, the group released their first soundtrack album The Collective Soul and Unconscious: Chapter One Original Soundtrack from "What Is Your B?". On February 11, 2022, it was announced that Billlie would be releasing their second EP The Collective Soul And Unconscious: Chapter One, featuring lead single "GingaMingaYo (The Strange World)" on February 23. The single is the group's first release to feature member Sheon. On December 14, the group released their first digital single album The Collective Soul and Unconscious: Snowy Night with "Snowy Night" as the lead single. On November 27, Sheon made a surprise appearance performing title track "Ring X Ring" along with the other members on South Korean music show Show! Music Core, marking her first appearance with the group. On November 19, it was announced that Kim Su-yeon, who had participated in Girls Planet 999, would join the group under the stage name Sheon (션) as the seventh member, and would officially join the group for their next album. On November 10, their debut EP The Billage of Perception: Chapter One was released featuring lead single "Ring X Ring" and five B-side tracks. A fan song titled "Flowerld", which was also included on the EP, was also released on the same day. On October 28, it was announced that their debut EP The Billage of Perception: Chapter One would be released on November 10. 2021–present: Debut with The Billage of Perception: Chapter One, "Snowy Night", and The Collective Soul and Unconscious: Chapter One Siyoon participated in the talent show K-pop Star 5 and also worked as a model for the magazine Popteen. Sheon participated in the Mnet survival program Girls Planet 999, and was eliminated in the final episode placing tenth. Additionally, Tsuki worked as a model for the magazine Popteen and released the single "Magic" with the modeling group MAGICOUR in 2020.

Haram and Tsuki are former SM Entertainment trainees. She also participated in the JTBC survival program Mix Nine and starred in the web drama A-Teen in 2018, and its 2019 sequel A-Teen 2. Suhyeon participated in the Mnet survival program Produce 101 placing 69th and eliminated in the fifth episode. She participated in the music competition program Unpretty Rapstar 2 finishing as the third runner-up. Prior to debut, Moon Sua was a YG Entertainment trainee for 10 years.

On October 11, It was revealed that the group would be called 'Billlie'. On September 14, Mystic Story announced plans to debut Mystic rookies in November 2021.

The members of Billlie were known as Mystic Rookies - a rookie development program under Mystic Story. The name also reflects their "B-sides, the inner-self that everyone has inside them", which they express in hope to empathize with the audience.

The number '11' came from their group's legend "When the 11th bell rings in the middle of a purple rain, something strange happens", where the members lie about what happened in order to keep the event a secret. The name Billlie is spelled with three Ls due to the fact that the name can be broken down into 'Bi' (Korean word for rain), '11', and 'lie' - Bi11lie. A seventh member, Sheon, later joined the group. The group originally consisted of six members: Moon Sua, Suhyeon, Haram, Tsuki, Siyoon and Haruna. Billlie debuted on November 10, 2021, with the extended play (EP) The Billage of Perception: Chapter One. Billlie ( Korean: 빌리 RR: Billi stylized as Bi11lie or Billlǃə) is a South Korean girl group formed by Mystic Story.
