Uguu became famous as the catchphrase of Ayu Tsukimiya in Kanon, the visual novel released in 1999 and adapted into anime in 2002 and again in 2006. Ayu says it when upset or flustered, and fans clipped the sound as a shorthand for cute sadness. It spread through anime forums, early YouTube edits and soundboards, and stayed popular because a single syllable conveys pouting disappointment in any context, even for viewers who have never watched the series itself in full.