Perhaps in the 'Steven Universe Watch the Future fanfiction', there could be a plot where Steven travels to a different dimension within the Gem universe. In this dimension, the rules are different, and he has to adapt quickly. He meets alternate versions of his friends who have different personalities or powers. This could lead to a self - discovery journey for Steven as he sees how different choices could have led to different outcomes. He then has to find a way to bring back something from this dimension that can help save his own world from a brewing disaster.
Perhaps past versions of the Crystal Gems meet their future selves. They could be shocked by how much they've changed, or they might learn valuable lessons from each other. The past Gems could see how their actions in the past led to the future they now inhabit, which could be a really interesting exploration of cause and effect.
One idea could be a crossover with "Adventure Time". Finn and Jake could visit Beach City and interact with the Crystal Gems. They could go on a mission together to stop a new threat that combines the magic of both universes.
One idea could be that Lars and Steven go on a space adventure together. They might encounter new gem species and have to work together to solve problems. For example, they could find a planet where the gems are in a civil war, and Lars and Steven use their unique skills to bring peace.
A more emotional plot could be an OC who was once part of the Homeworld gems but defected. They have a lot of guilt and self - doubt because of their past actions. In the fanfiction, they try to make amends by helping the Crystal Gems. But they constantly fear that their old allies will come after them. This internal struggle and their journey of redemption could be a really interesting story.
One idea could be that Naruto and his friends end up in the world of Steven Universe. They could team up with the Crystal Gems to fight a new common enemy that has the power - stealing abilities like Orochimaru and the ability to corrupt gems like the Diamonds' powers. Naruto's jutsu could be a new and strange concept for the Gems, and Steven could try to understand Naruto's ninja way.
Well, the OC could be a human - gem hybrid. This would make them an outcast in both human and gem society at first. But as the story progresses, some of the main characters like Pearl, Amethyst, and Peridot start to form a bond with the OC. Maybe they are all intrigued by the OC's dual nature and the way they navigate between the two worlds. This could lead to a harem - like situation where they all have different relationships with the OC, some more platonic, some with a hint of romance.
One idea could be Lars exploring a new planet full of strange, sentient plants that communicate through colors. He has to figure out how to interact with them to get the resources he needs for his ship.
Maybe Black Pearl discovers a hidden power within herself that is connected to a long - forgotten Gem technology. This power could be something that the other Gems either fear or desire. The fanfiction could explore how she deals with this new - found power and the reactions of the other characters in the Steven Universe world.
Perhaps Steven finds himself in a situation where he has to protect a number of characters, and in the process, they all fall for him. Like he could be on a mission to save some of the corrupted Gems, and as he heals them, they see his pure intentions and are drawn to him. This could lead to a harem where they all vie for his attention in different ways, some being more shy and others more bold in their affections.
A really interesting plot could be that a powerful Gem weapon is stolen and ends up in the Voltron universe. The Paladins find it and don't understand its power at first. Meanwhile, the Crystal Gems think the Paladins are the ones who stole it on purpose. So there's this initial conflict. But as they start to communicate, they realize there's a bigger threat behind the theft. A shadowy figure is trying to use the weapon to destroy both universes. So they must join forces to stop this threat. The story could explore how the different characters interact and grow to trust each other.