Dragon Force is set in the world Legendra, which lived in an era of prosperity under the watch of the benevolent goddess Astea, until it came under siege by the evil god Madruk and his armies. To stop him, a defender came in the form of the Star dragon Harsgalt, and his chosen warriors known as the Dragon Force. Unfortunately, personal disputes amongst the Dragon Force led to their downfall and left Harsgalt to face Madruk. The two faced in a fight to death, and Harsgalt, unable to kill Madruk, sealed him away until eight new chosen warriors could rise to permanently defeat him.

300 years later, the seal imprisoning Madruk has weakened and two of his Dark Apostles, Scythe and Gaul, have begun working towards his release. To ensure none would stop their master, the two of them manipulate the eight nations of Legendra into warring amongst themselves. Eventually, one of the monarchs will successfully end the war, though the events of how it occurs vary depending on the monarch. Regardless, each of the monarchs will discover that they are the eight members of the Dragon Force, and that the only way they can kill Madruk is by obtaining the Dragon Power left by Harsgalt.
Despite attempts to stop them by Scythe and Gaul, whichever monarch the player controls gains the power, and then has to use it to defeat Madruk's final apostle, a robot named Katmondo. Subsequently, Madruk's prison continues to weaken, allowing him to release his army of dragonmen. Despite his army's release, the Dragon Force fight their way to Madruk's prison and find his three Dark Apostles waiting for them there. Whichever monarch that has the Dragon power leaves to face Madruk, while the remaining seven fight the Dark Apostles, and defeat them despite the three becoming even more powerful thanks the seal on Madruk weakening. The monarch with the Dragon Power then faces and kills Madruk, finally ending his threat. Though the monarch's generals initially lose hope of them surviving, they are saved by Astea, who leaves the world to be governed by the mortals, saying it is time for them to stand on their own. Whatever events that follow during the credits vary depending on the monarch the player uses.