Rumble Fighter Wiki:Storyline

A long time ago, an evil spirit known as the Shadow King planned to conquer the world and consume everyone in it. Many fighters fought hard in trying to defeat the evil king, but unfortunately some could not overcome the evil and became consumed by his power. These consumed fighters were known as the Dark Guardians. The Shadow King was defeated when fighters captured his evil spirit with the Sacred Seals and placed it underground in a location known as "Resurrection". After the defeat of the Shadow King, the Dark Guardians disappeared into the darkness as they waited for the perfect opportunity to strike again.

The ancient Guardian fighters who fought and defeated the Shadow King, gathered together and handed down their special powers to others for the war against evil. These fighters placed their powers into entities known as ExoCores, so the power could be utilized in the future for other fighters if evil ever returns. Fighters known as "Guardians of the Seals" were given these ExoCore abilities to continue the fight against evil.

The only way to keep the Shadow King from resurrecting is by protecting the Sacred Seals that contains him. The Seals are the only entity that keeps the Shadow King from returning. To ensure that the Seals were never to be joined again, Guardians secretly placed the Seals throughout the world. The Dark Guardians however, soon discovered that destroying the Seals was the only way to resurrect the Shadow King. The Dark Guardians searched high and low throughout the lands to locate the Seals. Eventually the Dark Guardians were able to obtain and crush some of the Seals. With the power of the Seals beginning to weaken, the Shadow King was able to utilize some fo his powers to instruct the Dark Guardians to create corrupted ExoCores so that they can initiate an even more powerful attack to bring the Kings resurrection closer.

Currently there is a huge war of good versus evil in the fight for the Sacred Seals. With the Seals weakening each day, the hopes of victory for the Guardians are starting to slip away. In preparation for the very worst, a Rumble Fighter Tournament is being held to recruit the best fighters from around the land to aid in the great war. What kind of fighter are you?

Reference
http://wiki.ogplanet.com/rf/index.php?title=Intro