One common theme is friendship. Their bond, whether it's growing stronger or falling apart, is often explored. For example, many fanfictions show how they supported each other in their early days as sorcerers.
One great fanfiction is 'The Bond Beyond'. It delves deep into the complex relationship between Gojo Satoru and Geto Suguru. It shows their early days at Jujutsu Tech, their training together, and how their ideologies start to diverge. The author does an excellent job of portraying their individual personalities and the strong connection they once had.
One common theme is the power dynamic. Since Geto has strong powers in the Jujutsu Kaisen universe, exploring how that affects his relationship with the reader can be interesting. For example, he might protect the reader using his powers.
Obviously, Shoko is a main character. She is often depicted as a tough and resourceful girl with her own set of skills. Another important character could be Finn. Finn might cross paths with Shoko and they could either become friends or rivals depending on the plot. Jake, Finn's loyal dog, could also play a role, perhaps helping or hindering Shoko's plans.