One interesting fanfiction could be about Killua and Illumi's relationship evolving. Maybe Killua is trying to break free from Illumi's over - protective and controlling ways. They could end up having a heart - to - heart conversation where Killua makes Illumi understand that he needs to grow on his own terms.
A common theme is the conflict between their different paths. Killua wants freedom and to make his own choices, while Illumi is bound by the family's rules and expectations. Fanfictions often explore how they deal with this divide.
Another theme is the idea of an unorthodox relationship. They are both rather strange characters in their own ways, and fanfics usually show how their relationship is not like a normal friendship or romance. It's something much more complex and full of intrigue.
Well, 'Illumi's Bond with Killua' fanfiction is quite popular. It focuses on the complex relationship between Illumi and Killua. It shows how Illumi's actions towards Killua are not just out of cruelty but also because of his own warped sense of family loyalty. Another notable one is 'Illumi's New Purpose', where after certain events in the Hunter x Hunter world, he starts to question his role and embarks on a journey to find a new meaning in his life.
There's 'The Unlikely Alliance'. In this fanfic, Hisoka and Illumi find themselves in a situation where they have to work together. It shows their initial distrust but also how they gradually come to understand each other's strengths and weaknesses, which is really interesting to read.
To start writing your own Hunter x Hunter Illumi fanfiction, you need to do some research on the Hunter x Hunter universe in general. Know the rules of nen, the different types of hunters, and how the world functions. For Illumi specifically, study his family background. Maybe you could base your story on how his family's influence has shaped him in ways not shown in the original. Outline your story first, including the main conflict, the characters involved, and how you want the story to end. This will give you a clear roadmap when you start writing.
One plot idea could be that Illumi and Hisoka are forced to team up on a mission. Their different personalities - Illumi's cold and calculating nature and Hisoka's flamboyant and unpredictable one - would create a lot of tension and interesting interactions. Maybe they have to infiltrate an enemy stronghold and they constantly bicker about the best way to do it.
Over time, their relationship could become more complex. Illumi's loyalty to his family and Hisoka's self - centered goals might clash. But they could also find common ground in their pursuit of power. They might start training together, which would lead to a deeper understanding of each other. Hisoka could learn about Illumi's cold family upbringing and Illumi could understand Hisoka's obsession with fighting strong opponents better.
The Hunter x Hunter manga is unfortunately not complete. The author has faced various issues that have led to intermittent breaks and an unresolved storyline.