A common theme is the crossover of powers. For example, ninjas using Pokemon abilities or Pokemon having some ninja - like skills. Another theme is friendship. Just like in Naruto and Pokemon separately, the characters in these fanfics form strong bonds with each other, whether they are Naruto characters or Pokemon. Also, exploration is a theme. As Naruto characters enter the Pokemon world or vice versa, they get to explore new places and cultures.
One great Naruto - Pokemon - Janine fanfic could be 'The Janine - Pokemon Alliance in the Naruto World'. It's a really cool story where Janine, with her skills from the Pokemon world, teams up with Naruto characters. It has some exciting battles and interesting character interactions.
The theme of identity is also present. When Pokemon enter the Naruto world or vice versa, the characters have to re - evaluate who they are. A Pokemon trainer might find that the ninja way is something they can relate to, and a Naruto character might discover new aspects of themselves through their interactions with Pokemon. Also, the idea of protecting the world is common. Both Pokemon and Naruto characters are often fighting to protect their respective worlds, and in the fanfics, they may team up to protect a combined world from threats.
Well, it could be about Naruto in a world where he has some sort of god - like status in the Pokemon universe. Maybe he can control Pokemon in ways that no one else can, or perhaps he has unique powers related to Pokemon that are based on his ninja skills.
In a fanfic, Naruto turning into a Pokemon might also lead to some comical situations. Imagine Naruto, now as a Pokemon, trying to communicate with his friends in Konoha. He might have to use Pokemon sounds and gestures at first, causing a lot of confusion among his comrades. But eventually, they figure out a way to understand him, and it becomes a fun adventure for everyone.
From Naruto, obviously Naruto himself would be a main character. Sasuke could also be there, maybe he's initially skeptical about the Pokemon but then warms up to them. In the Pokemon world, Ash and Pikachu are must - haves. Misty and Brock could also show up to offer their expertise in Pokemon training.
One common theme is the exploration of new worlds. Since it combines Naruto's world with the Pokemon world, characters often explore different regions or areas that are a blend of both. For example, they might find a forest in Naruto's world that has Pokemon living in it.
The theme of discovery is also present. Mewtwo is discovering a whole new world in Naruto, with new rules, new people, and new powers. And at the same time, the Naruto characters are discovering this strange and powerful being from another world. It's about exploring the unknown on both sides.
You can try fanfic websites like FanFiction.net or Archive of Our Own. Just type in 'Naruto Pokemon Janine' in the search bar, and you should get a list of relevant fanfics. Some of them might be really good reads.
A really fun Naruto Pokemon fanfic concept would be a story centered around a Pokemon tournament in the Hidden Leaf Village. Naruto and his friends would enter the tournament with their Pokemon partners. They'd have to train their Pokemon in the ways of the ninja, teaching them things like stealth and quick - thinking. And at the same time, the Pokemon would teach the Naruto characters some of their unique skills, like how to communicate with nature better through the Pokemon's connection to it.