Gon and Killua would be obvious choices. They already have a great dynamic and their friendship could be further explored in a school setting. For example, they could be roommates and have to deal with each other's annoying habits while also training together.
You could also create an original character. This character could be a transfer student from a far - off land. They bring with them a different perspective on nen and hunting, and their presence shakes up the status quo at the school. They could befriend Gon and the others, and together they embark on new adventures within the school.
Another character that could be important is Ging. Since he is Gon's father and has a mysterious past and a lot of influence in the Hunter x Hunter world. In a fanfic, he might play a role in Sakura's story, perhaps guiding her or being an obstacle she has to overcome depending on the plot of the fanfic.
There could also be new characters created specifically for the fanfic that are part of the Fourth Royal family. These characters might have their own goals, like maintaining the family's power or trying to change the traditional ways of the royal family. They would interact with the existing characters in interesting ways, creating new storylines.
The main characters include Gon Freecss, a determined boy seeking his father. Killua Zoldyck, an assassin - trained friend of Gon. Kurapika, who is driven by revenge. And Leorio, a would - be doctor. Hisoka is also a very prominent character, though more of an antagonist, with his own strange and dangerous motives.
Since it's a fan - made story, the main characters could be new characters created by the author. However, it's also very likely that it involves some of the well - known characters from Hunter x Hunter. Maybe Gon and his friends are called upon to help a sick village and they find out about the poor man's rose as a possible cure. So Gon, Killua, and Leorio could be the main characters in this fanfic's story about the cure.
Gon could be a likely character. He is extremely determined and has a strong sense of justice. In a situation where he is faced with an impossible task, like saving a dear friend who is on the verge of death, he might be tempted to make a deal with a devil. Another one could be Hisoka. He is always seeking power and new thrills. A deal with a devil to gain some unique and powerful Nen ability would be something that might appeal to him. Killua is also a possibility. He has a dark past and has always been in a struggle between his good side and the assassin training he received. If he thought a deal with a devil could protect his friends or atone for his past sins, he might consider it.
It could be a rogue hunter who has his own twisted ideas about the use of Nen. This hunter might see Pokkle and Ponzu as obstacles in his quest for power and knowledge. He could try to capture them to steal their Nen abilities or the information they have about certain areas of the Hunter x Hunter world.
Gon would be a likely focus. His determination and simple - minded yet strong - willed nature could lead to some interesting time - travel related stories. He might be on a quest to save someone in the past or prevent a future disaster.
How about a character who is a master of disguise within the Hunter x Hunter world? They could have a Nen ability that allows them to not only change their physical appearance but also their aura and nen - type. This would make them very difficult to detect and could lead to some really sneaky and devious plotlines. For example, they could infiltrate enemy groups or steal valuable information without being noticed.
One possible plot could be that Killua decides to surprise Gon with breakfast in bed. He gets up early, sneaks into the kitchen, and tries to cook Gon's favorite meal. However, he's not very good at cooking, so there are a lot of comical mishaps. In the end, Gon wakes up to a messy kitchen but a very sweet gesture from Killua.
One idea could be a new student arriving at the Hunter School with a unique nen ability that no one has seen before. This student then has to prove themselves in various trials and battles against the existing students. For example, they might face off against Gon and Killua in a sparring match that tests not only their physical skills but also their strategic thinking.