Wonderhoy is the signature catchphrase of Emu Otori, leader of Wonderlands x Showtime in Project Sekai: Colorful Stage, the rhythm game featuring Hatsune Miku and other virtual singers. Emu shouts it as a cheerful greeting and rallying cry for her troupe's performances, and fans quickly turned the line into shorthand for her personality. Clips spread through fan edits, reaction videos and soundboards, where its recognisable energy made it easy to reuse outside the game. It remains popular because it works both as a character reference and a burst of excitement, even for viewers who have never played Project Sekai.