Old Gaia represents every fear to ever exist in every Digimon in the B/C Universe. Few have witnessed it and lived to tell the tale, and those who have described it as an extremely massive Digimon of untold size. Indeed, when compared to Sol there is hardly any size difference, and Old Gaia is never in a good mood after having been sent away due to it's continuously growing size. Old Gaia's most feared trait, however, is it's Grand Genesis Cannon it has built into it's mouth. Virtually everything to ever exist is destroyed by the laser's sheer power. If the Galactic Core is hit by this mighty laser, it is capable of ripping apart an entire galaxy and detonating entire stars. The cannon is powered by "pure energy", and is surrounded by the red rings of power. Sometimes the power source of it's eyes are needed to power the cannon, turning the eyes white. It wasn't always a giant destroyer, as it used to be much, much smaller in his Gaiamon stage. It used to be only 1,000 feet tall (About twice SuperMechadramon's height), and this is also the height he appears as in the games as well, but is only like that because whenever The Grand One summons him, his size is downgraded to be of a much safer size yet still be very large and massive. Apparently, a smaller, identical version of the Grand Genesis Cannon is built into The Grand One's helmet, or so it was known to be prior to The Grand One even testing the weapon's destructive power.
Early History[]
2,000 years prior to B/C's timeline, The Grand One was beginning his creation of the universe that B/C's timeline would exist in. Prior to creating any other Digimon, he digiconverted four Vemmon that all acted in unison. Over 2,000 years of training, they digivolved from these forms into a combined form of Snatchmon and then into Galacticmon. Old Gaia referred to himself as Young Gaia during this timeframe. Two other Galacticmon were cloned from his data.
The Dragoramon Incident[]
17 years prior to the present, Young Gaia was sent along with his two brothers to chase after the rogue Rainboramon that had escaped Shiramu Inc.'s headquarters with vital DNA he began to experiment on. After a 3 day and 3 night chase, only Young Gaia remained, and he was nearly destroyed by Rainboramon as he crash landed in the Adeventure 02 Universe, right in the middle of a park where Matt and Sora happened to be. After witnessing the true extent of Rainboramon's powers, Young Gaia gave Biyomon and Gabumon the ability to digivolve again and also gave Gabumon the ability to digivolve into the Super Ultimate ZeedGarurumon. As Matt and Sora were heading to find the others to stop Rainboramon, Young Gaia said to Matt to "Give my master's regards to the youngling several months from now...", referring to Matt and Sora's first born child.
The Grand One would give Young Gaia the power to digivolve into his newly finished Super Ultimate form Gaiamon, and since then, Young Gaia became Old Gaia as he digivolved into Gaiamon. After following to where Rainboramon was, he witnessed only the end of what was going on as Rainboramon was now Dragoramon and the crisis was over. Old Gaia left peacefully along with Dragoramon and Terranadrosus, and Old Gaia would never be seen again for several years, during which it would grow so massive he couldn't possibly fit in the Digital World anymore and was sent into space under the disguise of The Grand Destroyer.
The Gaiamon Incident[]
Old Gaia, after 17 years, reached a very massive size indeed, and still continued to grow. At this point he was the size of Sol and was a danger to everything in the universe at this point. Slowly approaching Sol as it's intelligence had decreased to a primitive state after so many years of exile, Old Gaia moved a little too close to Neptune's vicinity and nearly destroyed the Digital World until The Grand One showed up and knocked him clear out of the Galaxy, and possibly to another universe.
The D-Reaper Incident[]
Many years had also passed in the Tamers universe as well, during which Takato married Jeri as well, and they seemed happy until old memories started haunting Jeri; The D-Reaper was making a comeback. However, they'd soon be hearing more from Old Gaia rather than the D-Reaper for a while. Somehow, the D-Reaper returned to it's dangerous state and was returning to the real world. Regaining it's intelligence, the D-Reaper spread at an even faster pace than anticipated. The D-Reaper, however, did not seem to know what fear was; It was swiftly introduced to it when Old Gaia showed up very dangerously close to Earth. The D-Reaper began to panic, not knowing how to prepare for something so massive. Old Gaia's mouth opened when it reached close enough to Earth, as a large cannon formed in it's mouth, readying to fire it's almighty beam cannon of destruction.
However, Dragoramon showed up and made the D-Reaper into an even larger target for Old Gaia to hit, moving it into space as it was the size of Neptune now. The D-Reaper, feeling more powerful, was surprised to be restrained by something to tiny, and still felt fear as to Old Gaia's presence. The D-Reaper begins to question if Dragoramon's power is even that of a Digimon at all, but it reveals it is not, rather surprisingly. Calling itself simply "Dragora", Dragoramon let's Old Gaia fire the Gaia Genesis Cannon at the D-Reaper at full power since nothing was in the way for the cannon to accidently destroy. The D-Reaper was completely vaporized in an instant, and off far in the distance some explosion is heard as Old Gaia and Dragoramon both shield the Earth from the shockwave caused by the cannon's fire. Dragoramon departs soon after the shockwave settles, and Old Gaia is left to his own thoughts, with Dragoramon's only thoughts being "The Grand One seeked to destroy the D-Reaper for "target practice"..." in a rather emotionless tone, also one of the few times Dragoramon "speaks" in any way.
Now, however, Old Gaia posed a threat in his own way due to being something so massive and close to Earth at the same time. Instead of outright destroying Earth with all of it's massiveness, it regained it's intelligence it had years ago. Being able to see down to Earth to Takato and Jeri, immediately flashing back to Matt and Sora from 17 years ago. It's intelligence having returned, it makes it's way away from this universe's Solar system and made it's way back towards the Adventure 02 universe. Suddenly recognizing both couples as true love, he sought out Hope and Light into his existence to regain his missing intelligence, thinking the original DigiDestined are key to restoring his memories. In fact, The Grand One just so happened to be residing in the Adventure 02 universe at that point... Dragoramon had apparently recorded the Gaia Genesis Cannon in action, and presented the recording to The Grand One. The Grand One, calling the weapon a success, is unsure how to properly make use of it now.