A common theme is the exploration of Raiden's humanity. Since he is a cyborg, fanfictions often dig into how much of his human side remains. Another theme is the power struggle. Given the high - octane action in the game, fanfics often play with who has the most power and how it's obtained. Also, the idea of revenge is prevalent, as the title implies.
Perhaps there could be a story where some of the Metal Gear Rising characters are reincarnated as ninjas in the Naruto world. They retain their memories and abilities from their previous lives. Raiden, for instance, could be reborn as a member of a minor ninja clan. He would then rise through the ranks, using his unique skills and determination, and eventually play a major role in the events that shape the Naruto world, all while trying to figure out why he was reincarnated in this strange new place.
One great 'Metal Gear Rising: Revengeance' fanfiction is 'The Blade's Redemption'. It delves deeper into Raiden's internal struggles post - game. Another interesting one is 'Rising Shadows' which explores the side characters more thoroughly. And there's also 'Revengeance Reimagined' that takes the story in a completely new and exciting direction.
Another way they could interact is through a trading of skills. Naruto, with his ability to create multiple clones, could teach this technique to the Metal Gear Rising characters. In return, Raiden could teach Naruto some of his sword - fighting skills. This exchange of skills could create new and exciting combat styles for both parties and also help to build relationships between the characters from the two different universes.
One idea could be a crossover where the characters from Metal Gear Rising have to adapt to the world of RWBY. For example, Raiden could team up with Ruby and they could share their combat skills. Maybe Raiden teaches Ruby some advanced sword techniques, while Ruby shows Raiden how to use Dust in combat.
One common theme is the clash of different technologies. Metal Gear Rising has its advanced cybernetic enhancements and Mass Effect has its biotics and space - faring tech.
Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own or FanFiction.net. Just search for 'Metal Gear Rising Mass Effect crossover' and you'll likely find a variety of stories with different takes on how the two universes could interact.
Raiden and Ruby would be an interesting pairing. Raiden is a highly skilled cyborg ninja with his own set of morals and combat abilities. Ruby, on the other hand, is a young and determined huntress. Their interaction could be fascinating as they come from different worlds but share a passion for fighting for what's right. Raiden's experience could help Ruby grow, and Ruby's enthusiasm could inspire Raiden.