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 many 'HxH Illumi x Reader' stories, the reader has a special power that Illumi wants to use for his own purposes. However, as he spends more time with the reader, his feelings start to change from just using them to actually caring about them. This kind of story often shows the complex character of Illumi as he struggles between his cold - hearted nature and his new - found emotions.
One great 'HxH Illumi x Reader' story could be about the reader being a new hunter and Illumi taking an unexpected interest in them. Maybe he's intrigued by their unique nen ability or their fearless attitude towards the dangerous tasks hunters face.
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.
Another theme is power. Given that both are very powerful in their own ways, fanfics often deal with how they compare their powers, use their powers in relation to each other, or how their powers influence their relationship.