Often, in these types of fanfictions, the protectors' side would include the strategist characters. For example, Tactician Tom. On the brawlers' side, it could be the most powerful and feared ones, such as Crusher Kong. Their meeting would create a lot of tension as Crusher Kong's brute strength clashes with Tactician Tom's calculated plans.
Well, they might start off as rivals. The protectors could see the brawlers as a threat to the peace they are trying to maintain. Maybe there would be some initial skirmishes or misunderstandings between them.
Homer Simpson is very likely to be involved. He's the main character and his bumbling yet loveable nature can create a lot of comical situations in crossovers. For instance, if it's a crossover with 'The Flintstones', Homer would probably be trying to out - eat Fred Flintstone at the local diner.
Sakura would definitely be involved. As a medical ninja, she would be at the forefront of trying to heal Naruto. Sasuke might also be there, either helping in the fight that led to Naruto's injury or coming back to the village to see his old rival. Kakashi would also be around, using his experience to strategize how to protect Naruto while he's injured.
Definitely his friends from Camp Half - Blood. Percy Jackson, for instance, would be likely to be involved. He might be the one to find Nico when he's hurt or be part of the group that's trying to rescue him. Annabeth could also be involved as she is often in the thick of things and would use her strategic mind to help Nico when he's injured. Hazel, being his sister, is very likely to be there. She would be extremely worried and do whatever she can to heal or protect him.
Well, Sasuke could be involved. He might be the one who finds Sakura when she's hurt and has to deal with his feelings for her while trying to get her help. Naruto is also a likely character. He could be devastated by Sakura's injury and vow to get revenge on whoever caused it.
Theon Greyjoy is also a candidate. His identity and self - worth are often tied to his appearance. A headshave in fanfiction could be a way to explore his further degradation or, conversely, his redemption as he sheds his old self - image and tries to start anew.
Shinji is a very likely character. His complex relationship with his father and his role as the main pilot make him a prime candidate for time travel scenarios. He could go back in time to try and fix things or understand his father better.
The main ones are Harry and Ginny. But Fleur and Bill could be involved as well, sharing their own wedding experiences with the couple. Ginny's brothers other than Ron, like Percy, would be there in their formal robes. Percy might even give a speech at the wedding. Cho Chang could be an unexpected guest, showing that there are no hard feelings between her and Harry. And then there are all the Hogwarts professors, like McGonagall, who would be there to bless the union and make sure everything runs smoothly in the magical aspects of the wedding.
Iruka and Mizuki are also possible characters for role reversal in fanfiction. Iruka could be the one with some hidden, not - so - good motives, while Mizuki could be the kind - hearted teacher figure. This would turn the early Naruto story on its head, as Iruka was Naruto's first positive influence in the original series. The new dynamic between Naruto and these two reversed characters would open up a whole new set of story possibilities.
Definitely Hellboy himself. He's the central character from his own universe and would be the main connection to the crossover. Then, Batman is a likely candidate. His detective skills and his willingness to work with 'outsiders' would make him a great fit. He could be intrigued by Hellboy's nature and abilities.