Often, the character of Arima Kishou himself is a key element. His unique personality, his skills, and his role in the story's universe are central. For example, his calm and collected nature is something that many fanfics play around with.
Yes, there are likely fanfictions out there with such a concept. The Naruto fandom is vast and creative, and crossovers with historical or other fictional characters like Sasaki Kojiro are not unheard of. Some fans might be intrigued by the idea of Naruto having some sort of connection or admiration for Sasaki Kojiro and create stories based on it.
One common theme is the clash of different worlds. Since it's a crossover, there's often the idea of Kishou Arima's world in Tokyo Ghoul colliding with another fictional world.
Hey, let me recommend a Doujinshi novel by Go Soul to you. It's called Go Soul: Onmyoji System." The novel was mainly about a person named Light who transmigrated to the world of Go Soul and met his childhood sweetheart, Fujiwara Sasaki. The two of them went through many hardships together and finally got together. The author of this book was Jun Wushang, and the quality was quite good! I hope you like my recommendation. Muah ~
In some kaori x arima fanfictions, they might be in a parallel universe where their roles are slightly different. For example, Kaori could be a famous composer and Arima a struggling pianist. Their encounter then leads to a whole new chapter in their lives, filled with inspiration, love, and the magic of music.
Sure. One great 'arima kishou fanfic' could be 'Arima Kishou's Hidden Journey'. It delves into his character in a really interesting way, showing his internal struggles and his relationships in a new light.