X-MEN
- Wolverine would be pretty much the same as in the past three films. After promising to help Ororo around the Institute, being the rebel that he is, he misses several of the classes he's supposed to teach. Throughout the duration of the film, Wolverine would learn to become a team player and fully pledge himself to the Institute.
- Storm would have a large role like in X3. She would have taken over Professor X's position as head of the institute, but she would still be the field leader of the X-Men. Internal turmoils would reveal themselves in flashbacks of her past, including the day she saw her mother and father die.
- Iceman would be the leader of the Generation X squad (the younger students on the X-Men). He would lead his fellow teammates so that one day they will become the new X-Men. For right now, however, he is simply a member of the X-Men. He also still has Rogue issues. The two would, at some point in the film, split. He would go to Kitty for comfort.
- Beast would be a part time X-Men member and part of the staff due to his work at the U.N. He would still be fighting for mutant rights, this time however, on a global scale. He would have government inside information, giving his fellow X-Men teammates a heads up.
- Shadowcat would be second in command of the Generation X squad and, like Bobby, a member of the X-Men. She would be part of the love triangle seen in X3. However, when Bobby and Rogue break up, Kitty is forced to choose between her friend and the boy she likes. She picks Bobby, causing a rift between Rogue and Kitty.
- Colossus would have a much larger role, but he would not be a frontrunner. His emotions for Kitty are evident, but she ignores them, more focused on Bobby. Colossus and Angel form a friendship, feeling as they are the outcasts on the team.
- Angel would be the CEO of Worthington Labs in the beginning of the film, publically announcing at a press conference the termination of the production of the "cure". Feeling that he was not meant for this world of business, Angel reveals to the public that he is a mutant, hands his company over to the VP and flies away. He returns to Xavier Mansion, a full fledged X-Men member. He and Colossus form a friendship.
- Rogue would be haunted by her choice of taking the "cure". It is evident to Rogue and Bobby that the other students think of her as a "traitor" and that she doesn't belong there. Realizing that Bobby isn't there for her anymore, she leaves him and the mansion, fed up it all. She returns to her roots and sees her family. Everyone moved on without her. She meets Gambit, a mutant that she becomes infatuated with. It is during this time in Mississippi that she realizes her powers are steadily returning.
BROTHERHOOD
Magneto would slowly be regaining his powers, however, more quickly than Rogue due to his strength. He is currently living in the Morlock Tunnels in NYC, head of the community. He has a rivalry with the former leader Marrow, which eventually leads into a battle in which Marrow is defeated.
Pyro would not appear.
Mystique would be slowly gaining her powers back too, however, her body rejects the "cure", killing her in the process
Juggernaut would appear in the beginning of the film with the X-Men hot on his tail, in an attempt to capture him and bring him to the authorities for his involvment in the Alcatraz Island incident. He is captured and defeated, left by the X-Men in a huge block of ice.