'Onii-chan' is the Japanese honorific younger siblings use for an older brother, and it became a staple phrase in anime and manga culture for expressing affection, admiration or teasing dependence. Clips isolating the word spread on soundboards and in fan edits during the rise of moe anime fandom online, where short voice lines were reused as reactions. Variations like onii-chan onii-chan are still shared for the same effect. The sound remains popular because it instantly communicates a specific character dynamic without any visual context.