Definitely Naruto and Spider - Man. Naruto's energetic and determined nature combined with Spider - Man's quippy and heroic attitude makes for a great crossover. They could swap powers or team up to fight villains in both universes.
Kakashi is also a favorite in these crossovers. His intelligence and wide range of jutsu, especially the Sharingan, make him interesting. In Marvel, he could be like a mentor figure to some of the younger heroes, similar to how he was in Naruto. In DC, he could be an ally to the Justice League, using his skills to outwit villains. Sakura, with her medical and combat skills, can also be a great addition, perhaps working with the Avengers' medical team in Marvel or with Wonder Woman in DC.
Definitely Ultraman. He is a well - known Japanese superhero, and when combined with Godzilla in fanfic, it creates a great mix of super - powered action. Also, Gamera is often crossed over with Godzilla. They are both giant turtle - like monsters in their own rights, and the crossovers usually involve some intense battles over who is the more powerful or dominant one.
Definitely Bell Cranel. If he is crossed over into the Naruto world, his growth as an adventurer in Danmachi can be compared to the growth of a ninja in Naruto. His determination to become stronger is similar to Naruto's. Also, Ais Wallenstein is popular. Her combat skills and beauty would make for an interesting combination in the Naruto universe, perhaps having epic battles with Naruto's strong female characters like Tsunade.
Pokémon characters are often seen in doraemon crossover fanfic. Pikachu could interact with Doraemon in many ways. Maybe Doraemon could use his Memory Bread to help Pikachu learn new moves faster. And Pikachu's electric powers could be used to power some of Doraemon's gadgets in case of a power outage.
In Naruto - Scott Pilgrim fanfiction, Rock Lee is a character that many fans like to cross over. His unique fighting style based on pure hard work and determination would be really cool to see in the Scott Pilgrim universe. And from Scott Pilgrim's side, Wallace Wells could be a popular crossover character. His laid - back and sarcastic personality could create some humorous moments when interacting with the Naruto characters.
Probably Naruto himself would be a very popular character to cross over. His energetic and determined personality could bring a lot of action and drive to a crossover story. In Vampire Academy, Rose Hathaway could be another popular choice. She is strong - willed and a skilled fighter. When these two characters meet, there could be a great dynamic of them either competing or teaming up. Another popular character from Naruto that could be used is Sasuke. His brooding and powerful nature would contrast well with the vampires in Vampire Academy.
Harry Potter himself is often a popular choice. He can be thrown into the chaotic world of Warhammer and his skills and values are put to the test. Another is Dumbledore. His great wisdom and powerful magic could be an interesting match against the dark forces in Warhammer.
Fiona is also a top choice. Her relationship with Shreck in the movies gives a lot of material for crossovers. Fanfiction writers might explore how she and Shreck interact in different universes or scenarios, like in a world where they are not in the same fairytale but a different, more modern world.
Harley Quinn and Rey could be a popular crossover. Rey is a strong female character in Star Wars, and Harley Quinn has a very distinct personality. A fanfic could explore how Rey's determination and Harley Quinn's chaos - loving nature would interact, maybe they team up to take on a group of bad guys in a very unorthodox way.
Link is often a top choice as he is so well - known in the Legend of Zelda series. His courage and combat skills can translate well into the Harry Potter world. Harry Potter himself is also very popular for crossovers as he has a huge fan base. Additionally, characters like Ron Weasley could be fun to cross over. He could bring his humor and loyalty to the Legend of Zelda world, perhaps befriending Link and helping him on his quests.