The 31st volume of the SNK arcade game soundtrack series is released. It includes background music from "Ninja Commando", "Robo Army", and "Mutation Nation". "Ninja Commando" is a vertically scrolling action game in which players challenge merchants of death using a wide variety of attacks such as ninja techniques and special moves activated by shots and command inputs, as well as beast transformation usable by collecting scrolls (Alpha Denshi at the time, released in 1992). "Robo Army" is a belt scrolling action game in which players fight the robot army Hell Jeed to restore peace (SNK, released in 1991). "Mutation Nation" is a belt scrolling action game in which players defeat mutants writhing in a devastated world with exhilarating combo attacks and special moves (SNK, released in 1992). The background music from three NEOGEO action titles is delivered across two CDs. The booklet includes a column by Taiga Asaba from the game web media "Goziline".