In this kind of fanfiction, there could be a crossover where the Pokemon world's healing techniques are combined with Naruto's medical ninjutsu. Since there's the 'immortal' aspect, perhaps an elixir from the Pokemon world that grants immortality is sought after in the Naruto world. Also, the different regions in the Pokemon world could be like hidden villages in Naruto. Trainers from the Pokemon world could come to the Naruto world to learn about chakra, and Naruto characters could go to the Pokemon world to understand their unique powers.
In some fanfictions, they might explore how Ash's bond with his Pokémon is similar to Naruto's bond with his friends in the Hidden Leaf Village. Ash's journey to become a Pokémon master and Naruto's journey to become Hokage both involve growth, friendship, and facing challenges. They could learn from each other's experiences. For instance, Naruto could teach Ash some of his ninja stealth techniques which could be useful when catching Pokémon in the wild.
One interesting crossover could be the characters from Naruto using Pokemon moves in a battle. For example, Naruto could use Pikachu's Thunderbolt move in his own unique way. Another could be the Pokemon existing in the Naruto world and being used by shinobi for various missions. They might be used for scouting, like a Pidgeot flying over enemy territory, or for combat support, such as a Charizard breathing fire to fend off attackers.
One interesting crossover could be Naruto having to team up with a Legendary Pokemon like Mewtwo. Imagine Naruto's speed and combat skills combined with Mewtwo's psychic powers. They could face off against powerful villains from both the Naruto and Pokemon universes. Another could be a story where Naruto discovers a Legendary Pokemon egg and has to protect it while on a mission.
One interesting crossover could be Ash and his Pokemon traveling to the Naruto universe and having to deal with the ninja world's challenges. Maybe Pikachu uses its electric attacks against ninja techniques.
One interesting crossover could be the combination of Naruto's ninjutsu with Pokemon's unique abilities. For example, a character might use a Fire - type Pokemon's power to enhance a Fire - style ninjutsu. Another could be the idea of Pokemon existing in the Naruto world and being used in battles alongside ninjas. Maybe a Pikachu could befriend Naruto and use its electric attacks to help him in combat against enemies like the Akatsuki.
In this type of fanfiction, there might be a crossover where a Pokemon character somehow enters the Naruto universe. For instance, Pikachu could end up in the Hidden Leaf Village. When the Nine - Tails senses Pikachu's electric energy, it could be intrigued. This could lead to an adventure where Naruto and Pikachu have to work together. Maybe Pikachu helps Naruto control the Nine - Tails' power better using its own unique skills, like how it can store and release electricity.
One possible crossover in Naruto and Hellsing fanfiction could be the sharing of powers. For example, Naruto's ability to use chakra could be combined with the vampiric powers in Hellsing. Maybe a character from Naruto gets turned into a vampire and has to deal with the new powers and the moral implications in the Hellsing universe.
One interesting crossover could be Naruto characters trying to catch Pokemon. For example, Naruto might see a Pikachu and think it's some kind of strange new summon. He'd probably try to befriend it in his own energetic way. Another could be the Pokemon trainers coming to the Naruto world and being amazed by the ninja abilities. They might try to learn some ninja techniques, like how to walk on water or climb trees easily.
Well, in some fanfictions, the immortality aspect might lead to really cool plotlines. Imagine Naruto characters like Sasuke or Kakashi becoming immortal and interacting with Fairy Tail's immortal characters like Zeref. They could exchange knowledge about their different forms of power and how to control their newfound immortality. Also, the guilds in Fairy Tail and the ninja villages in Naruto could form alliances based on this new shared situation of having immortal members.
One interesting crossover could be a battle between Goku and a powerful Pokemon like Mewtwo. Goku's martial arts skills against Mewtwo's psychic powers would make for an epic showdown. Another could be Goku training with Pokemon to increase his speed and agility. For example, he might train with Pikachu to learn quick dodging techniques.