This cry belongs to Gigantamax Pikachu, the enlarged form of Pikachu featured in Pokemon Sword and Shield, where Pikachu's familiar electric-mouse voice becomes bigger and more exaggerated. Fans quickly noticed that one part of the cry sounds like a clear PEE, clipped it, and shared it on soundboards and in short videos. Its popularity has lasted because it is short, instantly recognisable to Pokemon fans, and funny without needing any context, making it an easy reaction sound for edits and streams.