Some concepts include the integration of different cultures from the crossover. If it's a crossover with a show set in a different culture, the fanfiction might explore how Star and her friends adapt to it. There could also be the concept of time - travel in the crossovers. Star might travel back in time to a point where the forces of evil had a different origin. This could change the entire course of the story and her understanding of the forces she's fighting against.
One interesting concept could be characters from different universes within the fanfiction meeting and interacting. For example, Star from 'Star vs the Forces of Evil' might meet characters from other popular shows. This can lead to unique storylines and character developments. Another concept could be the combination of different magical elements from the show and the crossovers. It can create new powers and challenges for the characters.
In genderbend fanfiction, the character designs can be really fascinating. The male version of Star might have different magical powers or a different style of using magic. He could have a more brash or bold approach compared to the original Star, which would lead to different plot developments when facing the Forces of Evil.
Some fanfics focus on the origin stories of the villains in Star vs the Forces of Evil. They might explore what made Toffee so evil or how Ludo became the way he is. By delving into these backstories, the fanfic can add more depth to the existing story. And there are also fanfics that center around the magic items in the show, like the wand, and how they could be used in different and unexpected ways.
Another possibility is a crossover with 'Avatar: The Last Airbender'. Star could end up in the Avatar world and learn about bending. She might team up with Aang and his friends to fight against Fire Nation soldiers who have somehow gotten a hold of some of Star's magic spells and are using them for evil.
One interesting concept could be the crossover of the two universes' magic systems. For example, how Star's wand magic might interact with the gem powers in Steven Universe. Another could be the character interactions, like Star and Steven teaming up to face a common threat.
There could be a fanfiction that puts Evil Star in a situation where she has to face her own good side. Maybe she gets hit by a spell that makes her see the consequences of her evil actions. This could lead to an internal struggle within her, and the story could explore whether she would change or double down on her evil ways. It would be really interesting to see how the writer develops her character in such a scenario.
One interesting idea could be exploring a darker side of Marco's character. Maybe he has some hidden powers or motives that are revealed in the fanfiction. Another idea could be his relationships with other characters in this 'evil' scenario. For example, how does his friendship with Star change when he takes on this new, darker persona.
A great plot point would be a mutual enemy. Suppose there is an even greater evil that emerges and forces Coco Star and the Forces of Evil to put aside their differences and work together. They would have to learn to trust each other, which would be very difficult given their history. Along the way, they would discover new things about each other's powers and motives, and this could lead to a change in their relationship even after they defeat the common enemy.
A great crossover idea is to put Star in a situation where she has to prove herself to the Avengers. Maybe she accidentally lands in the middle of an Avengers battle and they initially think she's a threat. But then she shows them her skills and they work together. Also, imagine Marco being friends with Spider - Man. They could exchange stories about their adventures and help each other out in their respective battles.
One interesting fanfiction could be about an alternate universe where Star and Marco's roles are reversed. Another might focus on a backstory for one of the minor characters like Pony Head. And there could also be fanfictions that explore what would happen if the magic in the 'Star vs. the Forces of Evil' world suddenly disappeared.
There might be a fanfiction that focuses on the backstory of the villains in 'Star vs Forces of Evil'. It could explore their motives and how they became the forces of evil in the first place. For example, it could show how Toffee's past experiences shaped his hatred for the Butterfly family.