One common theme is the struggle with pride. In the original series, both Shirogane and Kaguya are too proud to admit their feelings easily, and this is often explored further in fanfiction. For example, they might have internal battles about who should confess first.
There's also 'A Different Perspective'. This fanfiction offers a unique take on their relationship by showing their interactions from the point of view of a side character. It gives fresh insights into how others perceive their relationship and adds a new layer of complexity.
Friendship is a key element. Akira and Shirogane often rely on each other, showing strong loyalty. For example, in many fanfics, when one is in danger, the other will go to great lengths to save them.
In the fanfiction, Naruto could enter Kaguya's mind. He might discover her past traumas that led her to become so power - hungry and vengeful. By understanding her pain, Naruto could offer her forgiveness and a new path. He could show her a vision of a future where she is part of a united world, not feared or hated, but respected and loved if she changes her ways. This could be a powerful incentive for Kaguya to change.