Peridot is quite popular too. Her unique personality, especially her growth from a somewhat antagonist to a more friendly character, makes for great storytelling in crossovers. In a crossover with 'Ben 10', Peridot's technological knowledge could be paired with Ben's Omnitrix - related adventures.
Yellow Diamond is also quite popular. She represents the power and authority of Homeworld. Fanfictions might focus on her character development, for example, showing a softer side of her or exploring how she came to be so strict in her rule. Her interactions with other Diamonds and her role in the overall hierarchy of Homeworld are interesting aspects to write about.
The Diamonds are extremely popular in gem war fanfiction. Their power and their role in starting and perpetuating the war are fascinating to explore. Writers can delve into their motives, their relationships with each other, and how they react to the events of the war, whether it's through changing their views or doubling down on their actions.
Obviously, Goku and Steven Universe themselves are very popular. They are the main characters that people are excited to see interact. Their different personalities, Goku's bold and straightforward nature and Steven's empathetic and kind - heartedness, make for great chemistry.
Pearl would be an interesting character to include. Her grace and combat skills, combined with her complex backstory, could add depth to any crossover. In a crossover with a historical - themed show, Pearl's knowledge of different eras could create interesting storylines. Another interesting character is Garnet. Her fusion status and stoic nature can lead to unique interactions, especially in a crossover with a show that also has characters with dual identities or special powers.
One interesting storyline could be where Steven's gem powers interact with the magic in the Undertale world. For example, his ability to heal might have a unique effect on the monsters in Undertale. Maybe he could heal some of the more damaged monsters and in turn, they help him understand their world better. Another could be a story where the characters from both universes team up to face a common threat. The Sans and Papyrus from Undertale could join forces with Steven and the Crystal Gems to fight against a powerful enemy that is a threat to both their worlds. It would be really cool to see how their different fighting styles and powers work together.
Steven is definitely one of the most popular. Since he is the main character in the show, many fan fictions revolve around his further adventures and growth. Pearl is also quite popular. Her elegance, intelligence, and complex relationship with Rose Quartz give writers a lot to work with. Garnet is another favorite. Her stoic nature and the mystery behind her fusion are often explored in fan fictions.
One popular crossover is having the Crystal Gems from Steven Universe team up with the Avengers to fight a common enemy. For example, they could battle a powerful alien threat that neither group could handle alone. The unique powers of the Crystal Gems, like Garnet's future vision and Steven's healing powers, combined with the Avengers' superhuman abilities would make for an exciting story.
One popular trope is the fusion of Pokemon with the Gems from Steven Universe. For example, a Pikachu - like Gem or a Gem - powered Pokemon. It combines the unique powers and characteristics of both universes in an interesting way.
Lars himself is of course a must - he's the central character in 'Lars of the Stars'. Steven is also very popular as he has a strong connection to Lars in the original series. His positive attitude and unique powers can add a lot to the fanfiction. Sadie could also be included as she has a special relationship with Lars. Her character development and her own skills could be explored further in the fanfiction context.
One popular theme could be exploring different relationships. For example, how a female Steven would interact with the existing characters like Pearl, Amethyst, and Garnet. Maybe she'd have a different dynamic with them, bringing out new sides of their personalities. Another theme might be self - discovery. Since Steven in the original series has a journey of understanding himself and his powers, a female Steven could have a similar yet distinct journey, perhaps facing different challenges due to being female in the Crystal Gem world. Also, themes of friendship and loyalty are likely to be explored, as they are central to the 'Steven Universe' series.