Another way is to put her in different relationships. Let her interact with characters she didn't have much to do with in the original series. For example, if she were to meet some of the more radical anti - Britannian groups. Her reactions to their ideologies and methods could be used to show her growth and the evolution of her own beliefs. She could be conflicted between her loyalty to her family and her understanding of the oppressed people's cause.
One idea could be a story where Nunnaly discovers her hidden power in the Code Geass world. Maybe she has a special ability that was dormant all this time and it starts to surface when she is in a life - threatening situation. This could change the power dynamics in the story and her relationship with other characters.
Well, it might be that the granddaughter follows a trail of mysterious events that are somehow connected to Nunnaly and eventually leads her to him. Or perhaps she meets someone who knew Nunnaly and gets directions from them.
Another possibility is that a villain in the Naruto world tries to use Nunnaly for her unique knowledge or skills. The shinobi of the Hidden Leaf, including Naruto, would then have to protect her. In the process, Nunnaly could learn about the values of the shinobi world like loyalty and perseverance.
Naruto might be intrigued by Nunnaly's calm and gentle nature. He could introduce her to his friends in the Hidden Leaf Village. They could have conversations about their different worlds. For instance, Naruto could tell Nunnaly about his dreams of becoming Hokage, and Nunnaly could share her own hopes for a peaceful world.
The Black Prince's character could develop through facing various moral dilemmas. For example, he might be forced to choose between loyalty to his family and doing what is right for the greater good. This would make him question his values and beliefs, leading to growth.
First, consider her personality traits. Is she as calculating as Schneizel or more emotional? You can give her a distinct personality that sets her apart. For example, if she's more empathetic, it could lead to interesting conflicts with Schneizel's cold - blooded strategies.
Kallen might also develop a stronger sense of leadership. In a new time period, she may have to take on different roles and responsibilities. This would force her to grow as a leader. She could learn new strategies and ways of dealing with people, which she could then bring back to her own time to better lead the Black Knights.
Some fanfics with character watch focus on the minor characters in 'Code Geass'. For instance, they might look at the character of Rivalz. They could show his reactions to the events happening around Lelouch and how he is affected by the bigger picture of the war and power struggles. This gives a fresh look at the series from an often - overlooked character's point of view.
One common theme is the empowerment of Nunnally. In many fanfics, she is no longer just a damsel in distress but becomes a force to be reckoned with. Another theme is family bonds, especially between Nunnally and Lelouch. Their relationship is often explored in more depth, whether it's through Lelouch's efforts to protect Nunnally or Nunnally's attempts to understand her brother's actions. Also, the idea of changing the world for the better is quite common. Nunnally, with her unique perspective, often tries to make Britannia or the whole world a more just and equal place in these fanfics.
For the OC, start by defining their backstory. Where are they from? What experiences have shaped them? If they are from a lower - class area in Britannia, they might have a different perspective on the empire compared to Cornelia. Then, think about their goals. Are they seeking revenge, justice, or something else? As for Cornelia, explore her loyalty to Britannia deeper. Show her internal conflicts, like her doubts about some of Britannia's actions. Also, in their interactions, let their characters evolve. For example, if the OC challenges Cornelia's beliefs, she could start to question herself more, and the OC could learn to be more diplomatic from Cornelia.