The Planet Buster continues the story that was told in the first Brandish, depicting the events that happened three years after the evil demonic king was defeated in his lost kingdom, sunken deep underground. The player takes control of a young warrior named Ares, who wields a magical weapon - a powerful sword called the Planet Buster. One day, while traveling through a desert, Ares is captured by a warlock named Karl, who is after the powers hidden within the magical sword. Suspecting Ares might have some valuable information, Karl doesn't execute him, but takes away the Planet Buster and throws Ares into his underground prison. Now the primary goal is to guide Ares out of the huge prison full of various dangers, and get the mighty weapon back.