A long time ago, B-Da City was attacked by an evil force called the Dark B-Da (or dark beings) in their quest to control the entire Blue Solar System. The heroic B-Daman, drawing on their legendary powers and ingenious technology, were able to overthrow the Nol Arc Empire and restore peace to the universe.
One thousand years later, the Dark B-Da have finally returned to conquer the Blue Solar System and make it part of their dominion. A young B-Daman called Shirobon, with a strong sense of justice, becomes a defender of B-Da City. Along with the help of his friends, They join the battle against the Dark B-Da who have come to destroy their home!

(Source: Bomberman Wiki)