In creating a 'noble six crossover fanfiction', it's important to make the crossover believable. You can do this by establishing a logical reason for Noble Six to enter the other universe. For example, a scientific experiment gone wrong. Then, give Noble Six a clear goal in the new universe. If it's a crossover with the Final Fantasy series, maybe Noble Six has to find a way to get back home by using the magic in that world. Also, use vivid descriptions to bring both universes to life. Describe how Noble Six's armor looks in the new, perhaps more magical or fantastical, setting. This will draw the reader in and make the fanfiction more compelling.
First, you need to have a clear understanding of Noble Six's character. Know their strengths, weaknesses, and values. Then, choose the crossover universe carefully. Make sure it has elements that can interact well with the Halo universe. For example, if it's a crossover with the Cyberpunk genre, think about how Noble Six's military training would fare in a high - tech, dystopian world. Also, create a strong plot. Maybe Noble Six is on a mission to retrieve something important from the other universe.