This sound is associated with Monkey D. Luffy from One Piece, the long-running manga by Eiichiro Oda and its anime adaptation that began in 1999. Luffy’s smile is one of the character’s most recognizable traits, so short clips like this spread easily in anime edits, reaction posts, and fan compilations. People keep using it because it instantly communicates optimism, resilience, and goofy confidence, even in very short videos where a full quote or longer scene would slow the pacing.