A great plot could be that an ancient evil from Naruto's world has found a way to cross into the Steven Universe world and is causing chaos. The characters from both universes must learn to trust and rely on each other. For example, Sasuke could use his Sharingan to analyze the patterns of the corrupted gems' attacks, while Pearl could teach him more refined swordsmanship techniques.
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.
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.
Perhaps OK KO travels to Steven's universe and is amazed by the different types of gems and their abilities. He could learn from Steven about gem culture and in return, teach Steven some of his cool fighting moves. This could lead to them going on an adventure together to help a group of gems who are in trouble.
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.
A possible plot is that Naruto and Steven are summoned to a world where a prophecy states they will form a harem to bring balance. Each member of the harem has a special role or power related to either Naruto's world of ninjas or Steven's gem world. As they interact, there are comical misunderstandings due to their different backgrounds, but they gradually form deep bonds and work towards fulfilling the prophecy.
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.
Perhaps in the fanfiction, there is a threat that only the combined forces of the Naruto universe and the Steven Universe can stop. Naruto and his friends team up with Steven, Garnet, Amethyst, and Pearl. They have to learn to work together, with Naruto's combat skills and the Gems' unique abilities being essential in defeating the common enemy.
One plot idea could be that Markiplier's character is a lost traveler who accidentally lands in the Steven Universe world. He is mistaken for a new type of gem at first. The Gems try to figure out what he is while he is just trying to find a way back home. But as time goes on, he starts to care about the Gems and their cause, and decides to stay and help them against the Diamonds.
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.
A plot could involve a powerful villain that threatens both the Naruto universe and the Steven Universe. So, Naruto and Steven have to team up. Steven could use his healing powers on Naruto's friends who get injured in battles, and Naruto could use his Rasengan to break through tough defenses of the enemy. They could also exchange their beliefs and values. Naruto could teach Steven about perseverance and never giving up, while Steven could show Naruto the power of love and acceptance in a more in - depth way.
Well, one possible plot could be that Naruto somehow ends up in the world of Steven Universe. Maybe a strange jutsu goes wrong and transports him there. He could meet Steven and the Crystal Gems. Naruto's skills in combat and his never - give - up attitude would be really interesting to see in the SU world. He might teach the Gems some new ninja moves, and they could teach him about gem magic in return.