Nani is the Japanese word for what, and in anime it is often delivered as a sharp gasp when a character is caught off guard. This short Hatsune Miku vocal captures that same reaction in under a second, which is why it works so well in short-form edits and meme compilations. Like other brief anime reactions such as anime ahh, it needs no translation for viewers who already know the trope, and its clean, isolated vocal makes it easy to drop over gameplay, reaction videos and chat clips without muddying the original audio.