The theme of survival is often present. The world of Hunter x Hunter is dangerous, and as Killua's sister, she has to face many threats. Fanfictions may show her using her wits and any special abilities she has to survive. There are also stories where she has to deal with the consequences of Killua's actions or reputation, which adds another layer to her character development.
One common theme is family. Since she's Killua's sister, there are often stories about their family bond, like how she might be trying to free him from the Zoldyck family's more restrictive ways. Another theme is growth. She's often shown growing in power and wisdom as she experiences the world outside of her family's home.
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.
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.
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 fanfiction could be 'The Adventures of Killua's Little Sister'. It focuses on her learning nen abilities in a unique way, different from Killua. The story has a great plot that shows her growth and how she deals with the dangerous world of Hunter x Hunter.
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.
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.
Friendship is a very common theme. Gon and Killua have a strong bond, and many fanfictions explore how this friendship grows and endures different trials. For example, they might face a powerful enemy together and their friendship is what helps them get through it.
One common theme is growth. The reader often starts off as a relatively inexperienced character, and through their interactions with Killua, they grow both in terms of their skills as a hunter and in their personal relationships. For example, they might learn how to better control their nen abilities with Killua's help.
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.
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.