Girl group Billlie made its long-awaited return Monday with its first single, "Side-B: Memoirs of Echo Unseen."

The four-track package comes seven months since the release of its fourth EP, "The Billage of Perception: Chapter Three," in March.

Billlie's Haram, Tsuki, Siyoon, Sheon and Haruna on Monday held a press conference in Seoul ahead of the album's release later that evening. Moon Sua and Suhyeon are currently on a break due to health concerns and did not take part in the latest album.

"We're happy to be back with a new album. Here, we unfurl a new story that takes place in a different place and time from our original narrative," Haram said during Monday's event.

Since its debut, the group has followed the mystery story of "Billlie goes missing, on the day of the 11th when it rained purple" and has rolled out two album series -- "The Billage of Perception" and "The Collective Soul and Unconscious: Snowy Night" -- under it.

"Side-B: Memoirs of Echo Unseen" is a spinoff of the epic and follows Billlie as the group forays into a new world, expanding on its adventure-seeking universe.

Opening Billlie's multiverse is the album's two songs, main track "'Dang! (Hocus Pocus)" and side-track, "BYOB (Bring Your Own Best Friend)," the latter of which had been prereleased last month.

"Dang! (Hocus Pocus)" is a perky electro-pop anthem over which the band delivers a strong message about self-acceptance. The title resembles the imaginary bell that rings inside our mind -- and the exclamatory sound we blurt out -- when we break out of the box to realize that what we knew of ourselves was not everything.

"How I perceive myself may me different from how others do, and through this album, we wanted to portray that -- all the countless versions of myself is me," Siyoon said.

"BYOB (Bring Your Own Best Friend)," a more easy-listening disco track, came out on Sept. 23 and landed in the upper tiers of iTunes K-pop Top Song charts in many countries, including the US, UK, France and Japan. Its music video also reached 11 million views in just three days, reflecting global anticipation for Billlie's new music.

The package also includes English versions of the two songs -- the first attempt at original lyrics by the band, which Sheon explained comes as part of their efforts to connect closer with global fans.

Billlie debuted in 2021 as the first K-pop idol group produced by Mystic Story, a local label whose roster of artists mainly consists of singer-songwriters and vocalists outside of K-pop. The group returns absent of Moon Sua and Suhyeon, who are both on temporary leave due to health reasons.

Rather than being disheartened, the five of them said they took this as an opportunity to become a stronger team, ready to welcome back their bandmates when they are ready.

"Health comes first before anything. For Billlie to last long as a septet, we believed it was best the two members take their time to recover. We'll brace the team until the day they come back and we become a seven again," Siyoon said, adding they still keep in contact with the other two.

Reorganizing from a septet to quintet required extra work, but the lessons from it were more than worth the effort.

"I remembered how valuable every member is to the team. I was worried at first since Sua and Suhyeon played essential roles, but instead, I was reminded that Billlie is a team of seven members, all massively talented in their own ways," Haram said, adding, "'Dang!' with five members is great as it is, and I also look forward to the septet version of it."

Billlie hoped to thrive higher with the new songs. Sheon aspired for good chart scores, while Haruna hoped to win on TV music shows, adding, "Also, I really hope we win the 'best girl group award.'"

Siyoon, meanwhile, hoped to be cherished like a treasure by listeners, saying, "It's empowering when people cheer for us, saying they hope to hear us more. I hope that Billlie is loved more so that we could share more music with the people and perform on bigger stages."