Perhaps a fanfic where the Patriots from Metal Gear somehow gain knowledge of the Worm universe and attempt to control it. They could start by kidnapping certain parahumans and trying to weaponize their powers. Meanwhile, the heroes in the Worm world would have to figure out how to combat an enemy that is so technologically advanced and has such a complex understanding of control and manipulation.
Snake from Metal Gear would be an interesting character to feature. His combat skills, stealth, and ability to adapt to various situations could make for some great scenes in the Worm universe. In the Worm world, Taylor Hebert could also be a key character. Her experience with leading a team and her own unique powers would contrast well with Snake's more solo approach.
Perhaps the fanfic explores how the technology from Metal Gear might be incorporated into the RWBY universe. It could be about creating new weapons or gadgets for the RWBY characters using the advanced tech concepts from Metal Gear. This might change the power dynamics and the way battles are fought in the RWBY world.
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.
Perhaps a story where some of the Metal Gear technology finds its way into the Naruto world. Orochimaru might be interested in getting his hands on such advanced tech for his experiments. He could try to reverse - engineer it to enhance his own abilities or create new, powerful jutsu. And Konoha would have to deal with the threat of this new, unknown technology while also facing their regular enemies.
Perhaps a story where the Patriots from Metal Gear Solid are interested in the technology of Ghost in the Shell, especially the advanced cybernetic brains and how they could use it to further their control. The heroes from both sides would then have to team up to stop the Patriots' new scheme. This would involve a lot of action scenes with both the high - tech weapons from Metal Gear Solid and the cybernetic combat abilities from Ghost in the Shell.
One idea could be to have Taylor from 'Worm' end up in the 'Fate' universe and have to deal with the Grail War. Maybe she forms a pact with a Servant who is similar to one of her powers in 'Worm'.
One idea could be an OC who is a master of stealth technology, perhaps even surpassing Snake in some ways. They could be on a mission to uncover a new type of Metal Gear that has been secretly developed by a rogue faction within the military - industrial complex. Another plot could involve an OC who has a unique connection to the AI systems in the Metal Gear universe, and they have to prevent the AI from going rogue and causing global chaos.
One idea could be a crossover where the characters from RWBY have to adapt to the high - tech, cybernetic world of Metal Gear Rising. For example, Ruby could be fascinated by the advanced weaponry and try to incorporate some of the technology into her Crescent Rose. Another idea is a story where the villains from Metal Gear Rising are somehow transported to the RWBY universe and cause chaos, forcing the RWBY teams to team up with the heroes from Metal Gear Rising to stop them. A third idea might be a character - study type of fanfiction, focusing on how a character like Raiden would react if he found himself in the RWBY world with its unique magic and Grimm threats.
One idea could be to have Naruto characters infiltrate a Metal Gear - like facility. For example, Naruto's shadow clones could be used to distract the guards while Sasuke tries to find and disable the main weapon system, similar to how Solid Snake would operate in the Metal Gear Solid games.
Some fan fictions might also focus on the relationship between Snake and the environment. Since the game is set in a jungle, there could be stories about how Snake adapts to the jungle in unique ways, or how the jungle itself seems to have a sentience of sorts and affects the events of the story.