Born in ultra-ancient China and shrouded in myth, the monster Bagan was the ruler of earth, sea, and sky. The beast's legendary power was what brought it to the attention of a nefarious group of aliens plotting to conquer the Earth in the year 199X. Warping back in time, they retrieved the monster and enhanced its already great abilities to incalculable levels through the cellular fusion of both Godzilla's and King Ghidorah's cells - a process directly influenced by the stolen research of Professor Ogata, the foremost expert on Godzilla's cells and member of the Anti-Monster Defense Forces in the present day.
Its metamorphosis finally complete, the energy body housing Bagan's essence erupts into rounds of radiant white light... its transformation alone leveling structures in the surrounding area, including the National Diet Building. The three-horned demon emerges from the light, towering over Godzilla and glaring intently as its alien captors revel in its awakening and explain the mighty beast's ancient origins. Even with a mild cellular fusion buff using King Ghidorah's cells, the crew of the Super-X2 realize that Godzilla is completely outclassed by the aliens' trump card. And with their primary research lab destroyed, hope seems bleak... until Professor Ogata suggests the military's backup Super-X in Osaka be used to collect energy from resupply bases scattered across Japan. The plan is a timely one, but it remains the only option, and the backup Super-X is immediately dispatched.
Their speech complete, Bagan at last stirs, raining hell upon Godzilla. Despite his best efforts, the king of the monsters can barely scratch the surface of Bagan's thick armored hide. The three-horned monstrosity hardly flinches to any of Godzilla's physical attacks, as its weight alone makes it incredibly sturdy. Even Godzilla's signature Fire Breath Attack is rendered useless by Bagan's force field. Only when Godzilla taps into his inner power with a Hyper Breath Attack does Bagan's force field fall, but the damage is still negligible. The hybrid super-monster retaliates after each of Godzilla's attacks with devastating body strikes, quickly depleting Godzilla's energy and dropping his fighting spirit. The situation is made direr as Bagan unsheathes its electrically-powered Slasher Claw, and unleashes its energy-based Plasma Beam and Diamond Storm techniques - all of which do tremendous damage.
But just as victory is within reach for the invaders, the backup Super-X at last arrives! The metal fortress startles Bagan, sending the monster careening backwards, giving just enough time necessary for the Super-X to pump its collected energy reservoir into the battered Godzilla.
The effect is immediate: Godzilla begins to flash a deep purple, his size growing and shifting, spikes jutting from enlarged shoulders and glowing green patches of skin erupting from his chest and spines, until finally his body calms - and a near-unrecognizable new form stands in his place. The fusion between Godzilla and King Ghidorah's cells has been fully realized: Super Godzilla!
With this new transformation, Super Godzilla stands on equal footing with the devil beast Bagan. The two square off in a battle of epic proportions, neither holding back as they blast one another with supped-up techniques and land ground-quaking physical strikes. But in the end, humanity's savior in the form of Super Godzilla emerges triumphant. With a deafening roar, the mythical Bagan sinks into the earth as a beam of light engulfs him and the surrounding area. The red sky clears, and the tri-horned behemoth is no more. The aliens, distraught at these events, refuse to acknowledge defeat and begin to retreat. But the crew aboard the Super-X2 shoot the alien mothership down, bringing an end to their terror.
With the invaders defeated, Super Godzilla demorphs into his original form, and the operation box used to control him is destroyed after his violent battle. Instinctively, Godzilla heads back out to sea under the rising sun, and peace returns to the world. Bagan is never seen again.