Fate Shirou fanfic often focuses on his growth. He starts as a somewhat naive but determined character, and fanfics usually develop his skills and understanding further. For example, in many, he becomes stronger in combat or more adept at magic. Another characteristic is exploring his relationships. His bonds with other characters like Saber are often delved into more deeply, showing different sides of their connection.
Some fanfictions might focus on Shirou's struggle with his ideals in a more extreme way. For example, he could face a situation where his ideal of being a hero for everyone conflicts with the reality of the Grail War, and he has to make difficult choices that really test his beliefs.
There are also fanfictions that explore Sakura's darker side in relation to Shirou. Given her connection to the Grail and the secrets she holds, she could be a more complex and dangerous figure. However, Shirou's love for her might be the thing that tames or redeems her in these stories.
Another concept is a more comical crossover. Shirou tries to adapt to the different rules and magic in the Fate Apocrypha world. He constantly gets into funny situations as he misunderstands the local customs and magic systems. For example, he tries to cook using Apocrypha - style magic ingredients and chaos ensues.
It adds a new dimension to the characters. It shows different sides of Saber and Shirou that we might not see in the original work. This can make fans more interested in exploring their relationship further.
You can start by looking on popular fanfiction websites like Archive of Our Own or FanFiction.net. Use the search function and type in 'Fate RWBY Shirou Nikos'. Then, you can sort the results by popularity or rating. Another way is to join fan communities dedicated to Fate, RWBY, or both. Ask fellow fans for their recommendations. They might know some hidden gems that are not as easily found through general searches.
One interesting Fate female Shirou fanfiction could be 'A New Path for Female Shirou'. In this fic, it might explore how a female Shirou adapts to the complex world of Fate with her own unique take on the powers and relationships. It could show her interacting with other characters in a different way compared to the male Shirou, adding a fresh perspective to the story.
I'd recommend 'Rin and Shirou: Love in the Chaos'. It's a really good one. It shows how their love can endure even in the most difficult of situations. The writing style is engaging and it really makes you root for the two of them.
There are also fanfictions where their relationship has a more sudden start. Maybe a magical accident causes them to be linked in some way, like sharing emotions or thoughts. This forces them to understand each other on a very deep level right from the start. They then have to figure out how to deal with this new connection while also dealing with the challenges of the Holy Grail War, which in turn leads to a unique relationship development.
It could be Gilgamesh. Gilgamesh is extremely powerful and has a very different view of the world compared to Shirou. Their ideals would clash, with Gilgamesh seeing Shirou as a weakling with naive dreams of heroism, while Shirou would see Gilgamesh as a tyrant who needs to be stopped.