M.U.G.E.N. is a customizable 2D fighting game engine that allows users to create and implement their own characters, stages, and game modes. The phrase in question refers to the acquisition of this engine, configured or modified to include characters and elements from Japanese animation. For instance, one might seek to obtain a version populated with combatants from well-known series.
The appeal of this particular modification stems from the desire to experience interactive battles between characters from different anime universes, something not typically possible in officially released games. Historically, this activity has thrived within online communities dedicated to game modification and sharing fan-made content. This provides access to a diverse range of characters and allows for creative expression within the realm of fighting games.