Megaman Battle Network 4 Red Sun/Blue Moon
Duo was introduced in the video games, MegaMan Battle Network 4 Red Sun/Blue Moon, as the Final boss. Duo is the operation system for an asteroid-based rocket poised to destroy Earth. The villainous Dr. Regal attempts to control Duo, and the program itself acts as judge of the human race, deeming it evil and unworthy of survival. For this reason, Duo intends to destroy the planet, effectively eradicating the species so that there is not a single trace of evil energy left. Although his story essentially ends at the game's conclusion, he makes anonymous appearances in subsequent installments, usually providing players with exclusive Giga chips.
In the anime, Duo was a god-like entity, that was created by an unknown alien race. His main intention was to cleanse or destroy the world of all evil. The extraterrestrials that oversaw his genesis intended for Duo to expand their already vast computer network beyond the boundaries of their home planet, and he was therefore installed into a shuttle that was launched into space, eventually becoming a comet once it reached the outer limits of the atmosphere. Duo, however, defected from his original objective, as he felt that space did not require the network's useless influence, thus it was destined to be destroyed. From his comet, Duo laid waste to the planet, but not before some of its inhabitants escaped on a floating city, eventually landing on Earth during the age of the dinosaurs. Researching methods of halting "The Cybernetic God", the survivors came across a process similar to Cross Fusion, but were unsuccessful in completing a viable hybrid being, and only their city remained intact by the time it is discovered in Stream, shielded by technology akin to the "Dimensional Areas".
Duo's comet makes several trips to the Earth, crash landing thirty years prior to the events of Stream, and again fifteen years later destroying the airplane both Dr. Regal and Ms. Yuri (Yuriko Ozono) as children were traveling on. He turns the two into probes to monitor human life, then leaves them in the ocean to be found and raised by Dr.Wily. When Regal initiates a Dimensional Area that envelops the globe at the end of Axess, Duo is alerted to the chaos and sets off to perform "Earth Erasure". Giant viruses materialize in the real world and cause havoc, and ultimately the Earth ceases to exist. However, coming across Lan Hikari (Netto Hikari) and Chaud Blaze (Enzan Ijūin), he becomes intrigued by Cross Fusion and decides to spare the world so that it may prove to him that it merits survival. He reverts the damage caused by his advent, then marks thirteen individuals with the Crests of Duo, those chosen specifically for such a purpose.
Powers and Abilities
Duo has probably one of the highest HP in a Megaman Battle Network game. It can go as high as 3500HP. He possesses a huge variety of extremely potent abilities, many of them manifesting themselves in the form of space-age weaponry. His mighty fists are capable of crushing those that oppose him, and may detach through rocket propulsion to strike his enemies. His chest cavity houses explosive artillery, which is launched in either a direct or homing fashion, as either mines or missiles. This cavity may also compress in on itself to release a powerful focused laser beam that fans out at certain points along the spectrum. His most devastating technique involves expelling a flaming ball of energy, resembling a face, from his head.
Duo only has one weakness however, his chest cavity, and he can only be harmed when it's glowing red. He also can't be harmed by ground-based attacks, because he floats in space and there's no panels.
In the anime, Duo also possesses the ability to separate Navis and operators from Cross Fusion with a mere thought, allowing them to take on physical bodies while in his comet. Another ability he has in the anime is to edit DNA by chemotherapy, leaving the subject with supernatural powers like extremely high intelligence (like Dr. Regal) or the ability to survive and heal faster from heavily damaging physical experiences (like Ms. Yuri).