Maybe Ash gets lost in the Naruto world and Sakura finds him. At first, she's suspicious, but as she learns about his journey with Pokemon, she decides to help him find a way back. Along the way, they exchange knowledge. Ash teaches her about different Pokemon types, and Sakura shows him some new ninja techniques.
Ash could develop by learning from Sakura's more methodical approach to Pokemon. For example, he might start to study Pokemon habitats more carefully. Sakura, on the other hand, could become more adventurous like Ash, taking more risks in battles.
Well, imagine a scenario where a dark force is spreading across both their worlds. Ash and Sakura are chosen to be the ones to stop it. Ash brings his team of Pokemon, and Sakura brings her ninja skills. They travel through different regions, from the lush forests of the Pokemon world to the hidden villages of the Naruto world. Along the way, they meet new characters, some of whom join their cause, and others who try to stop them. They have to learn to work together, with Ash teaching Sakura about Pokemon training and Sakura teaching Ash some basic ninja moves.
Pikachu is a very likely candidate. It's Ash's most iconic Pokemon and has a deep bond with him. Whenever Ash is in trouble, Pikachu often steps up to protect him.
One interesting plot idea could be that Ash and Sakura team up to enter a special Pokemon tournament that features rare and powerful Pokemon. They have to train hard together, with Sakura's knowledge of different Pokemon types and Ash's battle experience combining to give them an edge.
Ash could be a Pokémon trainer with a different starting point in this fanfiction. Born in 1987, by 1997 he might have already made a name for himself in local Pokémon battles. He could have a team of Pokémon that he rescued from difficult situations, like a Charmander that was abandoned by its trainer. His story could revolve around giving these Pokémon a second chance and proving that Pokémon don't need to be 'perfect' to be strong.
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.
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.
When comparing their powers more closely, Ash's Pokémon can cover a wide range of elements and abilities. For example, a Charizard can fly and breathe fire, which gives Ash an advantage in aerial combat and against foes weak to fire. Naruto's powers are centered around his own body and chakra control. His Rasengan is a powerful close - range attack that can cause a lot of damage. However, if Ash's Pokémon can keep their distance, they could potentially outmaneuver Naruto. But Naruto's speed and agility from his ninja training could also give him an edge in dodging Pokémon attacks.
The impact of Ash's loss in the fanfiction could extend beyond just himself. His Pokémon might also feel demoralized. However, this could also be an opportunity for them to grow stronger together. Ash could start training more intensively, seek new training methods, or even try to catch new Pokémon to strengthen his team.