I shall leave this up for grabs unless I feel like getting around to it eventually.
It's the century of 20XX, the Classic era of Mega Man. It is about the time of Mega Man World V, some time after the mainline Mega Man 5 took place. Dr Wily has discovered a huge underground ruin filled with the remains of alien machinery and robotics. He discovered it by detecting that there was a layer of artificial rock beneath the top sediments, seemingly used to seal off a massive cave-in that took place over 20,000 years ago. Deep under a huge pile of rubble within this cavern, he finds a massive alien ship. Upon investigating, bringing along a couple of his rebuilt Wily Numbers from Mega Man 2, 3, and 5, Wily finds a massive robotic head in the core of the ship, seemingly scarred by a horrific attack in the distant past. He gets to work trying to fix it. In a few hours, he succeeds in sparking the giant robot head's internal power systems, and it begins to awaken with a rumbling screech. A series of metal crests fly from sockets on the walls nearby, embedding themselves in the heads of the Robot Masters, immediately subjecting them to a drastic transformation.
"These... these will do. Go, now... Bring it to me!"
Shadow Man, recently rebuilt as well but not brought along on the expedition, suddenly clutches his head and screams as a flood of long lost memories assault his processors. In a state of confusion and panic, he immediately leaves the current hideout Dr Wily uses and flees to parts unknown.
Some time later, Guts Man and Bomb Man are on the job at a large open air mine that's in the process of being decommissioned and refilled for land reclamation. Suddenly they get an alert from a bunch of small bots going offline in the same location. Before they shut down, it was like something had rapidly disassembled them with an unseen force. The two investigate to find a robot of strange and unfamiliar design appearing from the dust cloud that was stirred up from the ruckus, shambling forward mutely like a zombie. Its armor is a two-tone combination of dark and bright orange. Its shape is unlike any robot master, with small pointy lower legs, square shoulder armor, a cylindrical torso, a large crystal lens in the chest and on the back of each of its gauntlets, and a helmet vaguely giving off the air of a samurai with a three-pronged crest. Dangfling from the back of its head is a long chain made of green energy blades. Its eye sockets are dark and seemingly empty.
The two Robot Masters try to approach the strange bot, only for it to charge at them with extreme speed. It engages Guts Man in a brutal melee that few other robots would even consider challenging Guts Man in, fist flying with intense fury. The fight was quite brief, because the strange robot seemed to suddenly find itself drawn somewhere else after barely a few punches were thrown, immediately ditching Guts Man and Bomb Man.
Mega Man responds to a sudden mass robot attack at a major city, finding himself faced with an army of robots seemingly of totally different design from any known roboticist. All of these robots bear a distinct V emblem on the forehead. They are of a starkly higher quality than the robots typically sent by Dr Wily as fodder forces, coordinating like a military force. during the fight, Mega Man comes across someone wearing a cloak covering their entire body being surrounded by the enemy robots, and rushes to help them. Soon, the strange orange robot that attacked Guts Man and Bomb Man appears, eliminating the enemy robots with his blinding fighting style and brutal melee attacks imbued with an intense energy field. Notably, his eyes are lit up now, full of awareness and life in spite of lacking pupils like other advanced robots. He stares at Mega Man with tension, unsure of the other robot, while Mega Man keeps his buster ready.
The person in the shroud steps between Mega Man and the other robot, holding up a hand. The hand clearly belongs to a robot of the same type as the stranger, being made of segmented plates instead of a smooth glove covering the internal skeleton.
"You need not be so on edge. I don't think you two should consider yourselves enemies."
The cloaked robot pulls up his hood slightly, revealing a solid face plate and eyes hidden behind a pair of violet sunglasses. In spite of the hand appearing to be of similar design to the orange robot, the eyes behind the glasses almost look familar to Mega Man. The voice, too, is almost familiar, but that has clearly been modified as well.
"Your timely rescue is appreciated, Mega Man, and... Gravity Circuit."