Duo is a character from the Mega Man franchise.
- Note: Most info here is conjectural and based on opnions, not actual information.
In a galaxy far away from Earth, a planet with advanced technology habited with humanoid aliens was at war for centuries, its original cause being long forgotten, the people now fighting for trivial matters. During the war, a group of scientists sought to create something able to stop it and bring everlasting peace. Thus, after years of research and tests, a giant being whose body was mostly made of energy was created. At first, the being exceeded the expectation of his creators, ending the war in a week by destroying all weapons and beings that he considered dangerous or evil. However, due to them being at war for so long, the population could not get along well, and new confrontations started and were judged by it. As time passed, the being deemed that all living beings from the planet had evil within them, and disconsidering how good or evil they were, he destroyed his planet. With his home gone, it decided to travel in space to watch the development of different life forms and judge if they are good or evil, destroying them in the case of the later.
For millenia, he secretly watched several planets he discovered, with only three of the most advanced learning of his existance. Two of them kept track of his movements, which he didn't mind and learned to communicate with, and he was named "Duo". From one planet, five habitants were sent to follow Duo, one of them being Slur, while the other planet sent robots to watch him. Duo eventually began destroying planets, troubling his observers, but Duo explained that he was passing his judgement over planets that were hopelessly evil, and they had no need to fear him, but when Duo began destroying planets that had no apparent evil, including a planet that kept contact with one of his watcher's home, they knew Duo would eventually destroy them and allied themselves to stop him.
Duo saw it as a declaration of war, and disapproving it, decided to pass his judgement on these planets. Duo choosed to delay his decision over one of them (its habitants hadn't a high notion of good and evil, being mostly neutral and pacific), but the other two were destroyed. Except for Slur, Duo also finished with his observers, except for one that was useful for him, Slur. The remains from one of them was used to create Shadow Man. During his travels, Duo's history diverges greatly in two points.
Mega Man Battle Network series
When Duo left the third planet, its habitants were relieved that he didn't considered them evil, and they believed that Duo would not return again after passing his judgment. Unfortunately, they were mistaken. Centuries later, Duo returned to see how the planet was going, and his presence scared the population, who now thought that he was just a legend from past times.
Impressed, Duo decided to leave Earth, but he promised that he would return, and if it was not rid of evil, it would be destroyed.
Mega Man series
When Duo left the third planet, a great fear of him grew on its habitants, as they knew that he would return and do the same he did with the other planets. For centuries, they researched to prepare for the worst, advancing their technology beyond that of Duo's home planet and the other two destroyed planets, also incorporating technology from the two to their own. Their fears eventually became true when Duo was detected near their galaxy, and they entered in a terrifying war.
Duo and Slur were apparently destroyed, but the planet was severely damaged. (Several means would later be used to recover it or find other habitable planets, some of them, like the Stardroids and Constellation Droids, eventually reaching Earth.) Two days after the war, a massive energy sphere crashed on the planet, destroying a continent. When inspecting it, they discovered it was Duo, who was still alive and recovering despite his severe injuries. Although they did their best, the people from the planet could not completely destroy Duo (as he was on the planet, they could not use their most powerful weapons, and approaching Duo was difficult, let alone remove him), but they succeeded in splitting him into two parts.
The two parts were sealed into heavily watched robotic armors, also being used as the robots sole energy source in hopes that Duo would eventually dissipate, but instead, the energies had merged with the robots, basically becoming their "souls". Part of the memories and personality of Duo also combined with their programming, the two becoming twin beings different from the originals. However, before the merge, one of the robots was severely damaged inside by the original Duo and its programming was malfunctioning, causing it to be very different from his twin. They appeared to be identical, but one had a strong sense of justice while the other had destructive tendencies.
Hoping to permanently destroy Duo and wanting to avoid problems, it was ordered to have both destroyed, two new robots being created just in case. They fought against their captors, one trying to spare his attackers while the other went on a rampage. Noticing that one of them was only defending himself and didn't wish to cause harm, they decided to make Duo fight himself, offering to stop their attack if they also stopped. While one agreed, the other continued to savagely attack the others. Duo tried to calm him, but he was out of control and they fought. After calming down, the angry Duo asked why they should stop attacking as they are prisoners and should break free, but the other thinks they should not resort to violence when a pacific solution is possible. He reluctantly stops, and they are offered to live normally on the planet, but being secretly watched and analyzed.
After analyzes, it was discovering that the original Duo was no more, as the two became independant identities. One of the Duos was eventually accepted by the population, becoming an intergalactic police officer. The other Duo, however, was a trouble maker, never listening to orders. Not wanting to be compared with his twin, he bribed some persons to use parts from one of the other two robots built like them to change his appearance, increasing the power from one of his arms, and started building an army of robots, including Ra Moon as one of his commanders. When it was discovered, Duo tried to talk with his twin, but he was beaten and the evil Duo launched an attack to take over the city. To stand a chance against him, Duo was remodeled with parts from the other robot, including a bigger arm and an improved evil energy detector. A series of battles occur until the Duos faces each other, the battle resulting in the destruction of 70% of all life in the planet, barely avoiding destruction as the good Duo lured the evil Duo to fight in space. Their battle lasted for ages, eventually ending in a tie.
The two weakened warriors felt on Earth in Mega Man 8, were they are discovered by Dr. Wily and Mega Man. Thanks to Mega Man's help, Duo finally completed his primary mission to destroy the Evil Energy, and knowing that Mega Man can keep peace on Earth, he leaves the planet. Also, unknown to him, Ra Moon had traveled to Earth, and it was destroyed by Mega Man before his arrival on Earth. As the planet is similar to his original home(s), Duo decided to watch Earth for a while from space. When Earth was in crisis again, Duo returned to assist Mega Man a few times (Mega Man: Battle & Chase, Rockman Strategy, and Mega Man 2: The Power Fighters) before finally leaving the galaxy to travel for other planets that might need assistance.
- (discarted history plan)
Before being killed, one of them stated that "everything has good and evil within them, and you are not an exception. By destroying planets that contain evil, as consequence you also destroy all the good in it. Thus, would not that make you more evil than any planet you destroyed?" At first Duo didn't gave it much thought, believing it was only a lie from an evil being to escape him, but during his travels, Duo's history diverges greatly in two points.
Duo decided to pass judgement over himself, and while he isn't able to sense evil within him, he knows that killing isn't a good deed, and despite eliminating all evil, would he eventually also eradicate all good? Troubled with this, Duo attempt to remove his non-existant evil, and literally splits himself in two in the process. The original Duo was gone, but two massive energies were left. They were mostly equal, but one contained more of Duo's personality and memories, while the other had more of his power and all memories of planets being destroyed. As time passed, the former developed his own personality and becomes an intergalatic police officer, and the later, having a weak personality and destructive memories, was corrupted by his great power. They would eventually meet and fight each other, a battle that lasted for a long time until its end in Mega Man 8.