One day, the player’s character encounters Dan Kuso, one of the Battle Brawlers, who teaches him the rules of the game during a fight with Shuji. (You get a Serpenoid, a Juggernoid, and a Saurus based on the attribute you choose at the start of the game.) After visiting the local store and meeting Alice, who proposes that the player battle with other brawlers in the park to gain BP (Bakugan Points, the game’s currency), a peculiar Bakugan named Leonidas falls from the sky and becomes the player’s new closest buddy. (Leonidas’ attribute is determined by the attribute you select.) Leonidas is an unknown and hostile Bakugan who was produced by all of the lost Bakugan’s rage locked in the Doom Dimension.
Several people will emerge in the player’s fights, but at the same time, a Darkus user named Marduk wishes to take over all Bakugan alongside Vladitor, another Bakugan that appears unexpectedly. The seals that held Vladitor hostage in the Doom Dimension abruptly cracked once Naga obtained the Silent Core, and he escaped. Marduk is shown to have partnered with Hal G, Masquerade, and Naga to destroy the Battle Brawlers and rule over the planets and the Bakugan at the end of a tournament when Dan makes the player an official Bakugan Battle Brawler. The player must win the Ultimate Battle Tournament, which includes defeating Dan, Runo, Marucho, Julie, Shun, Masquerade, and a one-on-one battle with Omega Leonidas and Battle Axe Vladitor.
After the player prevails, Vladitor and Leonidas both vanish, claiming that they have little power left after the brawl. Later, the player discovers that Vladitor granted Leonidas his remaining strength, claiming that he deserved it, leading Leonidas to believe that Vladitor “wasn’t all awful.” The game concludes with the player hurling Leonidas into the air and yelling, “Bakugan brawl!”
