Perhaps they travel to a time when the Geass power was first created. Lelouch could try to change the nature of the Geass power to make it less destructive. This would involve him interacting with the original creators of Geass and trying to persuade them to modify it. Meanwhile, Nunnally could be learning about the history of their world from a different perspective, which would help them in their future plans.
Lelouch's character would likely become more cautious. Knowing the consequences of his past actions through time travel, he might think twice before making rash decisions. For example, he might not be as quick to use his Geass power without considering all the long - term effects.
A lemon fanfiction usually contains romantic or sensual elements. In the context of Code Geass, Lelouch and Nunnally have a complex relationship. In fanfiction, it might explore a different side of their bond, perhaps a more romantic or even unorthodox one. However, it's important to note that such fanfictions might deviate from the original plot and characterizations of the anime.
One can expect a re - imagining of their relationship. Since it's a lemon fanfiction, there may be some romantic or emotional scenes that are more intense than in the original. It might also focus on the characters' inner thoughts and feelings towards each other in a more intimate way.
One interesting plot could be Lelouch using his Geass ability in the world of Kaguya. Maybe he accidentally Geass - es someone in Kaguya's court, causing chaos among the nobles. For example, he could Geass a noble to publicly oppose a decree that Kaguya was about to issue. This would create a whole new dynamic as Kaguya tries to figure out what's going on while also dealing with her own political and romantic situations. Another plot could involve Kaguya being transported to the Code Geass world. She might use her intelligence and charm to navigate the complex political landscape there, and perhaps even form an alliance with Lelouch to achieve a common goal, like overthrowing a tyrannical regime in the Code Geass world.
There is a fanfic called 'Lelouch's Time Travel Adventure'. In it, Lelouch travels back in time to a point before the start of the series. He uses his knowledge of the future to try and prevent the events that led to the sad state of the world in the original story. It has some really cool moments where he outsmarts his enemies using future knowledge, and the way the author writes his internal monologues is very interesting, making it a great read for Code Geass fans.
Perhaps Nunnally's own perception of brotherly love is explored. She might start to notice the extreme nature of some characters' brocon - like feelings towards her. This could make her feel uncomfortable or, on the other hand, she might try to use it to her advantage in the complex political and social situations in the Code Geass world. The fanfic could then follow her journey as she deals with these new - found emotions and power dynamics.
One common theme is redemption. Since she's traveling back in time, the female Lelouch often tries to right the wrongs she did in the original timeline. Another theme is the exploration of different relationships. For instance, how her relationships with other characters change when she has the knowledge of the future.
One popular theme is Nunnally's growth and development. Since she has such an important role in the anime, many fanfictions explore how she could become stronger or more independent. Another theme is her relationship with Lelouch, whether it's a more in - depth exploration of their sibling bond or how she might react if she found out about his true identity.
Time travel can greatly expand Lelouch's character development. When he travels back in time, he gets a second chance. This makes him more cautious as he doesn't want to repeat the same mistakes. For example, he might be more careful in his relationships with Suzaku and others, knowing how things turned out before.
In Code Geass fanfic, Nunnally is often a complex character. She is usually depicted as a symbol of innocence and hope. Writers might explore her relationship with Lelouch in different ways. For example, some fanfics might focus on how she would react if she knew all of Lelouch's secrets and plans. Her blindness also adds an interesting layer to her character, as it can be used to show her inner strength and vulnerability simultaneously.