Another theme is adaptation. He has to adapt to the new rules, cultures, and powers of the crossover world. For example, if it's a crossover with a magic - based world, Naruto has to learn how magic works and how to use it. This theme of adaptation makes for some interesting character development.
They're popular because they offer a new take on the Naruto story. People like seeing how the relationship between Naruto and Sasuke changes when Sasuke is banished.
The plot might involve Naruto's unique abilities like shadow clones and Rasengan being combined with Nen abilities in the Hunter x Hunter world. For example, he could use his chakra to enhance his Nen attacks if he manages to learn Nen. And they could all be on a quest to find a way to get Naruto back to his own world while also dealing with some powerful villains who are interested in Naruto's power.
One common plot element could be Naruto being unjustly banished from the Hidden Leaf Village. Then, in the crossover aspect, he might end up in a different world or situation where he has to prove himself. Regarding Sasuke bashing, Sasuke could be portrayed as a villain or someone who betrays Naruto more severely than in the original story.
One great 'naruto banished crossover fanfic' is 'Naruto: The Banished Avenger'. It combines Naruto's banishment with a crossover to the world of 'Attack on Titan'. The story has some really interesting plot twists where Naruto uses his ninja skills in the Titan - filled world.
I'm not sure of specific fanfics with this exact theme off the top of my head. However, you can try searching on popular fanfic websites like FanFiction.net or Archive of Our Own. Use the relevant keywords in the search bar to find stories that might fit this description.
There's also 'Sasuke's Exile: New Beginnings'. In this fanfic, the banishment of Sasuke leads to a whole new set of alliances and power dynamics. It's great because it delves deep into the characters' emotions and how they react to this unexpected turn of events. The crossovers in it add an extra layer of intrigue as well, like when characters from other anime worlds start to interact with the Naruto characters due to Sasuke's banishment.
The characters' different power systems would also play a role in their interactions. Naruto might be curious about Nen and ask a lot of questions. Gon and Killua would be amazed by Naruto's chakra - based powers. They could also learn from each other. For instance, Naruto could teach Gon and Killua about his ninja training techniques, like stealth and quick - thinking in combat situations. And Gon and Killua could show Naruto how to better utilize his senses in battle, which is something they're good at in the Hunter x Hunter world.
To write a great Naruto banished married crossover fanfiction, start with a strong premise. Decide early on why Naruto is banished and who he is married to. Let's say he's married to Temari. The banishment could be because of a prophecy that some in Konoha misinterpret. For the crossover, if it's with a world of mythical creatures, research those creatures. Develop the relationship between Naruto and Temari. Maybe they have different views on how to deal with the new world they are in. Write engaging dialogue that shows their personalities and how they grow as a couple in this new and difficult situation.
One common theme could be the clash of cultures. Naruto's ninja culture and the Pokemon trainer culture are very different. So exploring how characters adapt to this new culture they're exposed to is a theme.