Love and loyalty are themes that are often explored as well. It's not always romantic love, but a deep, unwavering loyalty that might exist between them. Some fanfictions show how, despite their differences, they would still be there for each other in difficult situations, like when facing a common enemy or dealing with the challenges within their family.
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.
There's 'Illumi's Obsession'. In this fanfic, it delves deep into how Illumi's feelings for Killua are complex and often misunderstood. It shows how their interactions can be both intense and full of unspoken emotions. It's quite engaging as it plays with the psychological aspects of their relationship.
Friendship or brotherhood is also a big theme. Despite their differences, many fanfictions show how they support each other in their own ways, like Killua relying on Illumi's skills in certain dangerous situations and Illumi having a soft spot for Killua deep down.
One popular illumi and killua fanfiction is 'A Brother's Bond'. It delves deep into their complex relationship, showing how they interact beyond what's shown in the original work. It has some really interesting character development for both of them.
In Hisoka x Illumi yaoi fanfictions, the attraction between them could be based on mutual respect for each other's power. Hisoka is always seeking strong opponents, and Illumi is a very powerful assassin. Their interactions in the original work provide a rich source of material for fanfiction writers to develop romantic or at least deeply emotional relationships between them.
One popular trope is the 'enemies - to - lovers' scenario. Given their somewhat antagonistic relationship in the original story, it's a natural progression in fanfiction. Another is the 'forced proximity' trope, perhaps they are forced to work together on a mission, which then leads to the development of their relationship.
In 'killua x gon fanfiction', one characteristic is the exploration of their relationship in different scenarios. It could be in alternate universes where they face new challenges. Also, their friendship is often romanticized to some extent, with the authors delving into the unspoken feelings they might have for each other. Moreover, the fictions usually stay true to their personalities as shown in the original anime, while adding new layers to them.
Well, a very frequent theme is the exploration of power dynamics. Given Illumi's powerful and somewhat intimidating nature, the fanfictions often look at how the OC fits into that power structure. It could be that the OC is weak at first and has to grow to be on par with Illumi, or the OC might have a unique power that changes the balance. Also, love and redemption are common themes. The OC might bring out a sense of redemption in Illumi, or they might fall in love in a rather complex and interesting way considering Illumi's character.