The cue comes from Millennium War Aigis, a tower defense game in which players arrange units on a map before defending against waves of enemies. Mission start sounds are a familiar part of that loop, because each stage begins only after the player has finished placing units and choosing a strategy. Short clips like this one circulate on soundboards and in fan edits, where the cue is instantly recognisable to players even without any visuals. Its continued use comes from that shorthand: three seconds is enough to signal a new battle, a new attempt, or a fresh plan.