Vilgax from Ben 10 could be an interesting character to include. If he somehow gets his hands on a Green Lantern ring or the technology related to it, he could become an even more formidable foe. This would force Ben and the Green Lanterns to team up against a common enemy who has combined the power of both universes in a dangerous way.
Definitely Ben and Ash. Ben with his Omnitrix and ability to transform into different aliens brings a whole new dimension of power and adventure. Ash, on the other hand, has his experience and deep connection with Pokemon. Their interactions would be fascinating. For instance, Ben might be amazed at how Ash can communicate with his Pokemon without any high - tech device, and Ash could be in awe of Ben's alien forms and their powers.
Ax from the Animorphs would also be a great focus. He's an alien himself, so his perspective on Ben and his powers would be unique. He could compare and contrast his own Andalite abilities with Ben's Omnitrix powers. Plus, Ax is really intelligent and his knowledge of different species and technology could add a lot to the crossover story.
One possible plot could be that the Omnitrix somehow gets linked to the Green Lantern power source. Ben could end up with a new set of alien forms that are influenced by Green Lantern energy. For example, he might have an alien form that can create constructs like a Green Lantern but with its own unique alien twist.
Mewtwo could be a very interesting character in this crossover. Mewtwo is a powerful and intelligent Pokémon. In a fanfiction, it could be intrigued by Ben's Omnitrix and the concept of being able to transform into different beings. Mewtwo might initially see Ben as a threat or a potential ally in its own quest for power or understanding of the world. This could lead to some intense and thought - provoking interactions between Mewtwo and Ben.
Hinata would also be an interesting character to include. Her gentle yet strong personality and her Byakugan could offer a different perspective in the Killzone world. She might be more empathetic towards the Killzone characters. And from Killzone, Hakha could be a focus. His unique background and abilities could create some really complex and interesting storylines when combined with the Naruto characters.
I think Naruto and Spiderman are obvious choices, but also villains could be interesting. For example, Orochimaru from Naruto could team up with a Marvel villain like Doctor Octopus. Orochimaru might be interested in Doc Ock's mechanical tentacles and they could plot to take over both the Naruto world and New York. It would be up to Naruto and Spiderman to stop this unholy alliance.
Akagi would be a great character to focus on. His confident and sometimes over - the - top personality could bring a lot of humor and energy to a crossover. For example, if he was in a crossover with a detective anime, he might try to take charge of the investigations in his own unique way.
Definitely Naruto and Geralt. Naruto with his bright - eyed optimism and powerful ninja skills would contrast greatly with Geralt's brooding and more practical monster - hunting skills. Their interactions would be full of learning and cultural clashes. For example, Naruto might be shocked at how Geralt deals with certain 'monsters' that in Naruto's world could potentially be redeemed. And Geralt would be intrigued by Naruto's chakra and jutsu.
Definitely Naruto and Link. Naruto's energetic and determined personality would contrast well with Link's more stoic nature. They could learn a lot from each other. Also, Zelda would be interesting. Her wisdom and magical abilities would add a different dimension. And Sasuke could also be a great character to include. His dark past and thirst for power could lead to some interesting interactions in the Zelda world, especially when faced with the power of the Triforce.
Leonidas from '300' would be a great character to focus on. Imagine his reaction to the magic of the Harry Potter world. He's a fearless leader, and seeing him interact with wizards and magical creatures would be fascinating. He might see the magic as a new weapon or a strange form of sorcery that he has to either embrace or fight against.