Redemption is also a theme. Sometimes Erik has done things that he regrets, and Charles is there to help him find a way back. Or vice versa, where Charles makes mistakes and Erik is the one to offer support. This theme of forgiveness and growth is quite prevalent in many Charles x Erik fanfictions.
One common theme is the exploration of their relationship under new circumstances. The mpreg forces them to reevaluate their connection and face new responsibilities. Another theme is the protection of the unborn child. Erik often takes on a very protective role.
Often, there are themes related to their powers and how they interact with each other because of that. For example, how Erik's magnetic powers and Charles' telepathy play into their relationship. There are also themes about redemption, like Erik trying to make up for his past actions while being supported by Charles. And sometimes, the theme of them teaming up against a common enemy in a way that deepens their bond.
Often, you'll find themes like redemption in Charles and Erik fanfic. Maybe Erik has to find his way back from a dark path, and Charles is there to guide him. Also, the theme of loyalty comes up a lot. Despite their differences, they have a deep loyalty to each other in many of these stories. And there's the theme of sacrifice too. They might be willing to sacrifice their own beliefs or even their safety for the other.
One common theme is the struggle between their different beliefs. Charles often advocates for peaceful co - existence with humans while Erik believes in a more militant approach to protect mutants. Fanfics usually explore how they deal with this fundamental difference.
One common theme is the crossover of powers. Since Charles and Erik have mutant abilities and the Avengers have their own unique powers, fics often explore how these powers interact or clash. Another theme is the formation of new alliances. Writers like to play with the idea of how Charles and Erik would fit into the Avengers' dynamic.
One main theme is the discovery of self. Without their mutant powers as the main focus, Charles and Erik have to look deeper into who they are as individuals. For example, they might question their values and beliefs in a more normal world setting.
One common theme is redemption. Erik often seeks redemption for his past actions through his relationship with Christine. For example, in many stories, he tries to prove that he can be a better person because of his love for her.
One common scenario is when other mutants show an interest in Charles. Erik gets all possessive and tries to drive them away. For example, if a new mutant joins the X - Men and starts getting too friendly with Charles, Erik will make it clear that Charles is 'his' in a way. Another scenario could be when Charles is in danger. Erik's possessiveness kicks in and he becomes overly protective, not allowing anyone else to take charge of Charles' safety.
One popular theme is the struggle between their different ideologies while still maintaining their love. For example, their views on mutants and how to coexist with humans can create a lot of tension and drama in the stories.
A common theme is redemption. The OC often serves as a catalyst for Erik's redemption, helping him move away from his darker tendencies. Another theme is acceptance. The OC accepts Erik as he is, which is a big deal considering his appearance and past actions. For example, in many fics, the OC might be the first person to touch Erik's face without recoiling in horror.