Some fanfictions might introduce new original characters. These could be other robots or humans that interact with Mega Man and X. They could be scientists who help repair and upgrade them, or new villains created specifically for this fan - made encounter between Mega Man and X.
Obviously, Mega Man and X are the main characters. Mega Man is known for his classic platform - based adventures and his ability to copy the powers of defeated bosses. X, on the other hand, has a more advanced and complex backstory, being a more evolved form of Reploid.
There could also be other supporting characters from the Mega Man and X universes. For instance, Dr. Light might be mentioned as Mega Man's creator, and Dr. Cain could be part of X's backstory. Maybe Zero could also make an appearance as X's friend and ally, adding more depth to the story and potential for different plotlines.
Obviously, Rock and X are the main characters.
Dr. Wily could be the main villain. He might have found a way to travel through time or dimensions to the world of Mega Man X. He then uses his knowledge of Mega Man's weaknesses and combines it with new technology in the Mega Man X world to create even more powerful and devious robots.
Definitely Geo Stelar from Megaman Starforce and X from Megaman X. Geo has his own set of skills and X is iconic in his series. They would be the natural leaders to start interactions between the two groups.
A likely main antagonist could be a rogue scientist who has found a way to merge the technologies from both the Megaman Star Force and Megaman X worlds in a very dangerous way. He wants to use this new power to take over both universes.
Obviously, Megaman Starforce and Megaman Rock would be the main characters. They are the ones the title focuses on. Maybe their respective sidekicks or friends could also play important roles, like Geo's friends in Starforce and Rock's allies like Roll.
Obviously, Megaman Star Force and Megaman Rock would be the main characters. They are the key figures from their respective series.
The main characters are, of course, Megaman X from the Megaman series and Nana. Megaman X is a powerful robot with advanced combat abilities. Nana is a character with her own set of traits, which could be various things depending on the specific fanfiction, but generally she is a character focused on relationships and personal development.
Sigma could be the main villain. Since he is a major threat in the Megaman X series, his ambition to conquer and destroy could extend to the Megaman Star Force world once he realizes there are new forms of power and technology there. He could see the wave powers of the Star Force characters as something to be harnessed for his evil plans.
Dr. Wily could be a likely antagonist. He might be jealous of the new technology in X's world and try to take it over. Also, Sigma is a common enemy in the Megaman X series. He could see Rock as a threat to his plans of Reploid domination and target him. Another possibility is a new villain created specifically for the fanfiction, perhaps a mad scientist who wants to combine the technology of Rock's era with that of X's for evil purposes.
Perhaps in the fanfiction, Mega Man and Mega Man X meet in a virtual world created by a mad scientist. The virtual world is filled with distorted versions of their old enemies. They have to work together to find the core of this virtual world and shut it down. Along the way, they share their experiences and upgrade each other's abilities, leading to a new and more powerful form for both of them when they finally face the scientist.