The game's plot is set between Gradius III and Gradius Gaiden. Bacterion was developing a powerful weapon to use against the planet Gradius, but it was destroyed. A few years later it crashed on a planet and the planet gradually changed into a mechanical fortress. The planet Gradius then sent the Vic Viper to stop it.

The game's plot is set between Gradius III and Gradius Gaiden. Bacterion was developing a powerful weapon to use against the planet Gradius, but it was destroyed. A few years later it crashed on a planet and the planet gradually changed into a mechanical fortress. The planet Gradius then sent the Vic Viper to stop it.