Noise are monsters in the video game The World Ends With You. They dwell on a layer of reality normally invisible to living humans, but they form a vital component of the Reaper Game, in which the recently deceased participate for a chance to live again.
Noise are a naturally occuring phenomenon composed of negative human emotions. Largely mindless, they exist solely to reproduce, which they do by locating depressed or discouraged humans and exacerbating those emotions. This provides the material to create new Noise as well as attracting other Noise, leading to a vicious cycle of depression in their victim.
While most Noise are natural, they can also be created or summoned by Reapers, who use them to battle the players of the Reaper Game (the rules forbid Reaper-Player combat except under specific circumstances). Players must battle the Noise in teams of two. Noise exist on different dimensional layers simultaneosly, and each Player gets his or her own version of the Noise to fight. The Noise share damage and health across dimensions, so if one is destroyed (or "erased" in Game parlance) they are both destroyed.
Most Noise take the form of brightly-colored stylized animals, with some portion of their body appearing as a two-dimensional tribal tattoo. Taboo Noise, a more powerful variant created with special techniques forbidden from Reaper knowledge, are primarily black and gray. As they are exceptionally dangerous to Reapers and Players alike, their creation or use is a capital offense among the Reapers, hence their designation as "Taboo".