Yes, it is. As a 'Code Geass' fan, it gives you more content related to the series. You get to explore the story further and might discover new aspects of the characters and the world.
Well, fanfiction about Euphemia and Lelouch often explores their complex relationship. In the original Code Geass, their relationship was full of political and emotional entanglements. Fanfictions might expand on the unfulfilled potential of their relationship, like imagining a world where they could have overcome the barriers between them, perhaps in a more peaceful world without the chaos of war and power struggles.
Code Geass did start as a manga. However, its anime version became even more widely known and beloved. The manga provided the foundation for the rich story and characters that were further developed in the anime.
Code Geass started as an anime. The manga was based on the anime's success and came after to expand the story for fans. Some elements might differ between the two, but the anime was the original form.
Yes, there are quite a few. Some fanfictions explore how the magic from Harry Potter's world could interact with the political and strategic elements in Code Geass. For example, there might be stories where characters use spells to gain an edge in the mecha battles of Code Geass. However, the quality can vary greatly. You can find them on various fanfiction websites by simply searching for 'Harry Potter x Code Geass' in the search bar.