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.
One common theme in fanfics about Killua's sister is her growth and development. Writers may show her learning more about the world, becoming more independent, and perhaps even using her powers for good. She might go on adventures, similar to the main characters in Hunter x Hunter, and meet new and exciting people along the way.
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.
The themes usually revolve around family as well. His complex relationship with the Zoldyck family is often explored. Some fanfictions show him trying to reconcile with his family or completely break away. Adventure is another common theme. Since he's a Hunter, fanfictions often send him on exciting adventures, facing new monsters and challenges, which is in line with the spirit of the original 'Hunter x Hunter' series.
One great Killua's sister fanfiction is 'The Sister's Bond'. It delves deep into the relationship between Killua and his sister, exploring her character in new and interesting ways. It has some really engaging plot twists.
Friendship is a very common theme. Their strong bond is often explored further in fanfictions. Another common theme is growth, as they both grow in strength and character throughout the original series, and fanfictions like to expand on that. Adventure is also common as they are hunters.
Another theme is power. In many fanfictions, Killua's sister is portrayed as having unique powers or abilities that she has to learn to control. This could be related to her assassin training or something entirely new. It adds an interesting layer to her character.
A key characteristic is the development of their characters in a romantic light. In the original series, they have a strong friendship, but in yaoi fanfictions, it's taken further. They might have more vulnerable moments, like Gon sharing his insecurities with Killua in a more intimate way than in the original show, which adds depth to their relationship.
One common theme is growth. Biscuit often serves as a mentor to Killua, so a lot of fanfics focus on his growth in strength and character under her guidance.
One great Killua and Gon fanfiction is 'The Bond Beyond the Hunter Exams'. It delves deeper into their friendship right after the exams, showing how they support each other in learning new Nen abilities. Another one is 'Journey with Killua and Gon' which takes them on an adventure not shown in the original anime, exploring a mysterious island filled with unique creatures. And 'Killua and Gon: The Unseen Training' focuses on their intense training sessions and how it strengthens their bond.