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.
I think Pikachu and one of Ben's most used alien forms like Four Arms would be interesting. Pikachu is so iconic in the Pokemon world, and Four Arms is strong and has a unique personality. Imagine the battles they could get into together. Also, Pikachu's electric attacks could interact in unexpected ways with Four Arms' brute strength. And if they faced a common enemy, they would have to learn to work together despite their very different natures.
Professor Oak and Grandpa Max would be great characters to focus on. Professor Oak has his vast knowledge of Pokemon, while Grandpa Max has years of experience dealing with aliens and otherworldly threats. They could combine their knowledge to figure out how to handle the situation in a crossover. Maybe they start researching the similarities between Pokemon and the aliens from Ben's world, and their discussions could lead to some really interesting plot developments, like finding a way to use Pokemon powers to enhance the Omnitrix or vice versa.
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.
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.
Naruto would be the most interesting. His energetic and head - strong personality would make for great interactions with the Pokemon world. He could be constantly amazed by the different Pokemon and their abilities, yet still use his ninja skills and quick thinking to adapt. His ability to make friends easily would also mean he'd quickly bond with his Pokemon and other trainers.
Ash and Four Arms would be a great pair. Four Arms is all about brute strength, and Ash has his knowledge of Pokemon and his own battle skills. They could work together in battles against powerful foes. Maybe Ash could learn some new fighting techniques from Four Arms, and Four Arms could learn about the subtleties of Pokemon battles. It would be a clash of two different but equally cool fighting styles.
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.