Nin nin comes from Blue Archive, the Japanese mobile role playing game first released in 2021, where ninja themed characters and playful voice lines are a recurring part of its school setting. The phrase itself is a long used Japanese shorthand for ninja movement, often heard in anime and games. Clipped from in game audio, it spread through soundboards, short edits and chat replies because it is instantly recognisable in under a second. Like Tuturu, it survives as a short repeatable catchphrase that signals a character type without needing any setup or context.