A possible plot could be that Ash and Kari are transported to a strange dimension where the rules of Pokemon and Yu - Gi - Oh Zexal are all mixed up. For example, Pokemon battles can be influenced by Yu - Gi - Oh Zexal cards. They have to quickly adapt to this new environment. As they explore, they find out that a powerful being is behind this strange dimension and is planning to use it to invade the normal Pokemon and Yu - Gi - Oh Zexal worlds. Ash and Kari then have to find a way to defeat this being and return to their own worlds. Along the way, they make new friends from both universes and learn new strategies for battles and duels.
Well, a cool plot might be that Kari discovers she has a hidden ability to communicate with Pokemon, which is very rare in the combined world of Pokemon and Yu - Gi - Oh Zexal. Ash helps her understand and develop this ability. Meanwhile, they encounter a powerful villain who is using corrupted Pokemon and Yu - Gi - Oh Zexal cards to create chaos. They then journey to find a way to purify the villain's creations and restore peace. Also, maybe they meet some characters from both franchises who are also on a quest, and they join forces.
One idea could be exploring the backstories of the minor characters more in - depth. For example, what led them to become duelists in the first place. Another could be a time - travel plot where a character goes back to a crucial moment in the Zexal universe's history and changes something, leading to a whole new set of events and challenges. A third idea is to create a fanfiction where the main characters have to face a new, unknown type of duel that tests their skills and relationships in ways they haven't experienced before.
In this kind of fanfiction, Ash and Kari are the central characters. But from Pokemon, Serena could be included. She has her own dreams and skills related to Pokemon performances. In Yu - Gi - Oh Zexal, Tori would be a good addition. She's a friend of Yuma and can bring in the perspective of someone who is learning about dueling. Also, Gary from Pokemon could be added. His rivalry with Ash can add some tension and competition. And from Yu - Gi - Oh Zexal, Bronk can be included. He's a regular guy trying to improve his dueling skills, which can create some relatable moments in the story.
A plot could be where Dark Mist has a premonition about a future danger to Yuma. He tries to warn Yuma, but Yuma is initially skeptical. As events unfold, Yuma realizes that Dark Mist was right all along and they must team up to prevent the disaster. This could involve battles against new and powerful foes.
Another concept is a fusion of their powers. Suppose a villain creates a device that combines the power of the tailed beasts from Naruto and the Numbers from Yu - Gi - Oh Zexal. The heroes from both universes have to work together to stop this new threat. Yuma could use his ability to communicate with his monsters and Naruto could use his Sage Mode to sense the new evil power.
Another fanfiction could explore the backstory of a Barian female. How did she come to be in the Barian world? What were her experiences growing up there? This could involve her relationships with other Barians, her training, and how she developed her skills. It could also show how she first heard about the Yu - Gi - Oh Zexal world and what her initial thoughts were.
One idea could be a crossover where the Pokemon trainers and the Duelists from Yu - Gi - Oh 5ds have to team up to stop a common evil. Maybe an organization is trying to use both Pokemon powers and Duel Monsters for their own dark purposes. The trainers and Duelists would need to learn from each other's skills and strategies.
Maybe the reason for Yuma's kidnapping is not what it seems at first. Instead of being for his dueling abilities, it's because he has a hidden power that he's not even aware of. This power could be the key to saving or destroying the world of Zexal, and the kidnappers want to control it.
One interesting crossover could be the use of magic spells from Harry Potter in the Yu - Gi - Oh Zexal duels. For example, a character might use a spell to disrupt an opponent's summoned monster. Another aspect could be the interaction between the different magical creatures in both universes. Maybe a Hippogriff from Harry Potter could be a powerful ally in a Zexal - style battle. Also, the concept of Hogwarts houses could be incorporated into the Zexal world, with characters being sorted based on their personalities and duelist styles.
One possible plot could be that Naruto somehow gets transported to the Yu - Gi - Oh Zexal world. He might meet Yuma and his friends. Since Naruto is a ninja with unique skills like shadow clones, he could help Yuma in his duels. For example, Naruto could use his clones to distract opponents while Yuma figures out his strategy. Maybe they team up to face a common enemy who is causing chaos in both the ninja world and the Zexal world.
One idea could be Ash and Kari teaming up to stop a new threat that combines the chaos of the Pokemon and Digimon worlds. Maybe a villain is creating hybrid creatures and they have to use their combined knowledge and skills to stop it.