Another possibility is that a Marvel hero, say Spider - Man, accidentally ends up in Beach City. He teams up with Steven to deal with a local threat that is also related to some sort of interdimensional chaos. For example, a group of villains from the Gem world and the Marvel world are working together to open portals to other dimensions to steal valuable resources. Steven and Spider - Man would have to use their unique abilities to stop them.
Perhaps the Infinity Stones and the Gems have some sort of ancient connection. A crossover could explore how the characters from both universes figure out this connection. Captain Marvel and Garnet could be the ones to first sense the link. They then gather other powerful characters from both sides, like Steven and Iron Man, to understand and protect this connection from those who would abuse it for power.
Steven would probably be in awe of the high - tech world of Marvel at first. He might befriend Peter Parker (Spider - Man) easily as they are both young heroes with a strong sense of responsibility. Peter could teach Steven about some of the science - based superhero stuff, while Steven could show Peter his Gem powers. For example, Steven could create a shield out of his Gem powers similar to Captain America's, and they could compare how they work.
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.
To write this kind of fanfic, start with a strong hook. Maybe start with Steven waking up in the Underground or Frisk arriving on Earth near Beach City. Then, build the story gradually. Show how the characters react to the new environment and each other. Don't forget to add some action and conflict. It could be a battle between the Gems and some of the more aggressive monsters from Undertale. And make sure to stay true to the essence of both universes. Don't change the core personalities of the characters too much. This way, fans of both shows will be able to enjoy your fanfic.
One great idea could be a crossover between the X - Men and the Avengers. Imagine Wolverine teaming up with Captain America, their different fighting styles and moral compasses would create an interesting dynamic. Wolverine's rough - and - tumble, lone - wolf approach contrasting with Captain America's more traditional leadership and sense of justice.
A great fanfiction could be about Steven and Connie swapping bodies. This would lead to a lot of humorous moments as they try to figure out how to act like the other. Connie would struggle with Steven's powers, and Steven would have to deal with Connie's more studious and disciplined life. It could also be a chance for them to understand each other on a deeper level.
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 common concept is the character interactions in steven universe crossover fanfic. Writers often like to see how Steven would get along with characters from different shows. For instance, if there was a crossover with My Little Pony, Steven might have interesting conversations with Twilight Sparkle about magic and friendship. Some fanfics also focus on the world - building aspect, like how the Gem world would merge with the world of another show in a crossover.
One common theme is the exploration of different cultures. In both Steven Universe and Homestuck, there are unique cultures. In crossovers, it's interesting to see how the Crystal Gems' way of life and values interact with the trolls' or the kids' in Homestuck. For example, the idea of friendship and loyalty is strong in Steven Universe, and it can be contrasted or combined with the relationships in Homestuck.
A possible Undertale and Steven Universe crossover fanfic could be really interesting. It might involve characters from both universes meeting in a strange new world. For example, Steven could end up in the Underground from Undertale. He would probably try to use his powers of peace and love to resolve conflicts there, like how he does in his own show. Maybe he'd meet Sans and Papyrus, and there could be some really funny interactions. Sans with his laid - back attitude and Steven's positive energy would make for a great comical duo.
Another idea is that there is a fusion between a Pokemon and a Gem. This fusion could have a very distinct appearance and abilities. It could struggle to find its place in both the Pokemon world and the Steven Universe world. The story could then revolve around how it tries to fit in and how the characters from both universes react to this new and strange being.