In addition to the well - known Avengers, there might be some new or less - known characters. Maybe some characters from Iron Man's rogues' gallery could show up. Or perhaps a new hero that is related to Iron Man's technology in some way. There could also be some side characters that are important for the development of the story, like Pepper Potts who has a close relationship with Iron Man.
Obviously, the Avengers members like Iron Man, Captain America, etc. And the Warrior 3 which include Fandral, Hogun and Volstagg.
The Arrow is sure to be a main character. In addition, Hawkeye would be a crucial character in this fanfiction. Since they both are archers, there could be a lot of interaction between them, like competing or collaborating in archery - related tasks. And of course, Captain America with his leadership skills would also be among the main characters to lead the team that now includes the Arrow.
In addition to Naruto and Sasuke, Kakashi could play a significant role. As Naruto's mentor, he would need to guide Naruto in controlling and using his new body of steel. He might also be concerned about how this power will affect Naruto's growth as a ninja. Sakura could also be there, perhaps using her medical skills to study Naruto's body and understand the nature of this new power.
Captain America is a likely candidate. He has a strong moral compass and a sense of protectiveness. He would see it as his duty to take care of the baby. His old - fashioned values would make him a great caregiver, like making sure the baby has a proper upbringing even in the middle of all the chaos in the Avenger's world.
The central character would be the Avenger of Shinjuku. But also, there could be characters who are the Avenger's former allies or enemies from their past. In Shinjuku, we might see some ordinary citizens who get caught up in the chaos caused by the Avenger. There could also be other Servants who are in Shinjuku for their own reasons, such as seeking power or fulfilling a personal quest, and end up interacting with the Avenger.
The 'avenger of steel fanfic' could also have an interesting plot. It might involve a new villain or a different threat that forces the Avengers to work in new and unexpected ways. For example, it could be a threat that is not physical but rather something that targets their reputations or their unity as a team.
It's probable that the main characters are the Avengers we know and love. However, in this fanfic, their characterizations might be different due to the'steel' aspect. Maybe Iron Man is more focused on developing steel - based weapons for the team. Thor's connection to steel could be explored, perhaps his lightning has an effect on steel in this universe. Hulk could have a new form that is related to steel in some way. And of course, there could be original characters who are central to the story, like a steel - forging dwarf (inspired by Thor's world) who helps the Avengers create new weapons and armors out of steel.
Ichigo would probably be one of the main characters. He's the protagonist of Bleach, so it makes sense for him to be at the sleepover. Rukia might also be there, as she has a close relationship with Ichigo. And Uryu could be there too, since he's another important character in the series.
It could still be Naruto himself. Since he's the central character in the original series, many fanfics would likely continue to build on his story.
Well, obviously Corvo would be one of the main characters. He would bring his own set of skills, like his combat abilities and stealth techniques. Then, from RWBY, Ruby Rose could be a main character. Her leadership skills and scythe - wielding combat style would contrast and interact with Corvo in interesting ways.