First, choose the other fictional world to cross with Fablehaven carefully. Then, find a common threat or goal. For example, if crossing with a superhero universe, the common goal could be to stop an evil force that is after the magical artifacts in Fablehaven and also wants to take over the city in the superhero world. Next, think about how the characters from both worlds will interact. Will there be conflict at first? Or immediate cooperation? Finally, build up the tension and resolution throughout the story.
Start with a strong premise. For example, if you're crossing One Piece with the Attack on Titan world, maybe the devil fruit users are seen as a threat by the Titans. The plot could revolve around the devil fruit users trying to find a way to coexist or fight back. This gives a clear goal and conflict.
A good plot would also involve some sort of conflict. It could be a conflict between Ichigo and an antagonist in the 'Dangai' world who sees Ichigo as a threat. Or it could be an internal conflict within Ichigo as he adapts to the new environment. For example, he might struggle with the different rules of power in the 'Dangai' world compared to his own.
Perhaps there could be a situation where the magic in both Inkheart and Fablehaven is being drained by an unknown force. The characters from both worlds realize they need to find the source and stop it. Mo and Kendra could be the leaders in this quest. They start exploring different areas of both worlds, with the help of Dustfinger's knowledge of Inkheart's magic and Seth's familiarity with Fablehaven. Along the way, they discover that the two worlds are more connected than they thought, and there are ancient spells and artifacts that can help them. They face many challenges, like dangerous magical creatures and traps, but they keep going because the survival of both worlds depends on it.
First, choose the crossover universe carefully. If it's a 'Harry Potter' and 'Hunger Games' crossover, for example, you could start with a situation where the wizarding world has been overrun by a dark power that decides to use the Hunger Games concept to control the remaining wizards. Harry and his friends have to participate to survive and find a way to overthrow this new regime. Keep the core values of both universes intact.
A unique plot could involve the T - 3000 being reprogrammed by an unexpected force from the other crossover universe. This new programming could give it a whole new set of goals and morals, which would completely change its role in the story.
First, research both universes thoroughly. Know the capabilities of the Halo Spartans, their weapons, and the political situation in their world. Similarly, understand the powers, backstories, and relationships of the Overwatch characters. Then, find a common ground for them to interact. It could be a threat that affects both universes or a shared goal like exploring an ancient artifact that has significance in both worlds.
Research the uke concept and find ways to integrate it into Naruto's world. If the uke is often seen as a more submissive role, Naruto could be forced into that role due to some sort of magic or new social order. But he could still fight against it in his own Naruto - like way. You could also introduce new characters that are key to the uke - Naruto dynamic, like a powerful antagonist who misinterprets Naruto as weak because of the uke - like situation.
Combine different magic systems. For example, if crossing with the Magicians world, mix the Hogwarts magic with Brakebills' magic. The champions could struggle to adapt to new spells and incantations. Another way is to change the nature of the tasks. Instead of the usual tasks, make them more like a detective mystery where the champions have to solve a magical crime to progress in the tournament.
First, study the lore of both games. Know the rules of how powers work, the social structures in each world, etc. Then, find a common ground. Maybe it's a shared threat like a powerful, otherworldly entity that is attracted to the unique energy signatures of the powers in both universes. Make sure the characters' actions are in line with their personalities. For example, Cole is often driven by a sense of justice, so he would likely approach a situation differently than Alex, who has more of a survival - of - the - fittest mentality.
Start with a character from an unexpected universe getting invited to the Tournament of Power. For instance, a character from a fantasy world where magic is the main power source. Then, as they enter, they face challenges not only in the battles but also in understanding the technology and different power systems in the Tournament of Power world.