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.
This statement implies a certain sense of fatalism among soldiers in Code Geass fanfiction. It shows that they are aware of the high risks involved in their profession. In the complex power struggles and battles depicted in the series, soldiers are caught up in a web of events where death is a very real possibility. Their job, in this view, is not just about fighting but also about being ready to sacrifice their lives for the greater good or the mission at hand. It also reflects on the themes of loyalty, honor, and the cost of war that are often explored in Code Geass fanfiction.
First, study the existing world of Code Geass. Know the politics, the social hierarchy, and the technology. For example, if your OC is a Britannian, they should act according to the values and norms of that society. Second, give your OC a clear motivation. It could be revenge, love, or a desire for power. And third, don't make them overpowered. Even if they have a special ability, it should have limitations.
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.