"Nani" is the Japanese word for "what," and its dramatic delivery became widely recognized through anime reaction clips shared in meme videos and short edits. Online creators turned the shouted version into a reusable button sound for moments of disbelief, confusion and sudden shock. It spread across YouTube, Discord soundboards and short-form social posts because the line is brief, instantly readable and easy to time with a hard cut or zoom. Its popularity lasts because it communicates an exaggerated reaction in less than a second.