Megaman Star Force and Megaman Rock are the main ones. But we can't forget about the potential of other important characters. In the Megaman Star Force series, characters like Geo Stelar who transforms into Megaman Star Force could bring his own set of skills and relationships into the story. In the Megaman Rock world, other robot masters might be involved too. They could either be allies or be under some sort of mind control that Megaman Rock and Megaman Star Force have to break to get them on their side. Also, any characters related to the backstories of either Megaman could play a role, like the people who created them or those who have been important in their development.
Obviously, Megaman Star Force and Megaman Rock would be the main characters. They are the key figures from their respective series.
The main characters would surely be Megaman Star Force and Megaman Rock. However, there could also be some supporting characters from their individual universes. For instance, in the Megaman Star Force world, there might be some of his friends or allies that come along to help in the new adventure. And in the Megaman Rock world, maybe some of the classic characters like Roll or Dr. Light could make an appearance, either to offer advice or to contribute in some way to the fight against the common enemy.
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.
The plot could involve the characters from Megaman Star Force and Megaman Rock coming together to face a new common enemy. Maybe they start off as strangers in different digital worlds but are brought together by some strange glitches that are affecting both their realms.
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.
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.
Obviously, Rock and X are the main characters.
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.
One possible plot could be that the characters from Megaman Star Force find themselves in the world of Megaman X. They could team up to fight a new common enemy that is a threat to both their worlds. Maybe a powerful virus that is corrupting the cybernetic systems in both universes.
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.
Well, it could be about the two Megamans teaming up to fight a common enemy. Maybe they combine their unique abilities, like Starforce's EM Wave powers and Rock's classic weaponry, to take on a powerful villain that threatens both of their worlds.
One key element is the contrast between Rock and X. Rock is more of a classic hero from an earlier era, while X has a more complex backstory. Their different personalities often lead to interesting interactions. Another element is the merging of their worlds. Since they come from different parts of the Megaman universe, how the fanfiction writer combines their settings is important.