The sound comes from Attack on Titan, the anime adaptation of Hajime Isayama's manga that premiered in 2013, where Eren Jaeger is the central protagonist voiced in Japanese by Yuki Kaji. As the story grew darker, short clips of Eren's unstable laughter were isolated by fans and shared across YouTube, TikTok and soundboards. Editors kept returning to it because it instantly communicates a character losing control, so it moved beyond anime fandom into general reaction memes about betrayal, rage and villain arcs.