A in C major (ラ音) is a musical note that is heard when players are temporarily drawn into The World or The World R:2, often coinciding with the appearance of an AI or other abnormality unrelated to normal gameplay. The tone usually goes unnoticed by those who hear it, though Mai Minase, an experienced musician, was able to identify it and, once conscious of it, avoided its effects, which seem to subliminally distract the player and blur the line between reality and The World.