On March 26, 2026, MAMAMOO’s Moonbyul dropped a new Instagram post, showcasing her unique charm as she struck energetic poses alongside several artists — hinting at a bold new challenge. She tagged '#문별', '#MoonByul', '#REV', '#Hertz', and '#Hertz_Challenge', instantly sparking fans’ curiosity. In the photos, Moonbyul and her colleagues pose in front of a door backdrop in a variety of dynamic shots. Fans flooded the comments with excitement, writing things like "5muses omooo ㅋㅋㅋ" and "YOUNGJI AND SEULGI IN THE SAME PLACE???"