The sound comes from Project Sekai: Colorful Stage, the rhythm game built around Hatsune Miku and original characters, where Ena Shinonome is a member of Nightcord at 25:00 and Mizuki Akiyama is her close friend and bandmate. Fans clipped Ena yelling Mizuki's name and shared it as a standalone reaction sound, where it spread through edits, fan videos and short-form posts. It remains popular because the shout needs no translation or setup, and it instantly signals urgency, exasperation or playful blame among fans of the game.