Hisoka is another character that could be a focus. His unpredictable and chaotic nature could make for some wild time travel adventures. He might use time travel to find stronger opponents in different eras or to manipulate events for his own amusement.
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.
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.
I think Hisoka could also be involved in tickle revenge in some strange and twisted fanfictions. Hisoka has his own unique sense of 'fun' and if someone were to tickle him as a way to mock or play with him, he would surely retaliate in a very Hisoka - like way. Also, Illumi might be involved if it's related to his brother Killua. If someone were to tickle Killua in a way that Illumi thought was inappropriate or dangerous, he might plan a tickle revenge on behalf of his brother.
Kurapika could also be a likely character. Given his intense and often self - sacrificing nature in his pursuit of revenge, his friends would want to take care of him. Leorio, in particular, would be the one to bring him breakfast in bed. It could be a moment of respite for Kurapika from his heavy burdens, and a chance for some heart - to - heart conversation with his friend.
Tony Stark is a likely focus. His intelligence and experience with technology, especially time - travel technology in the movies, make him a central figure. He could be the one to figure out the mechanics of time travel and lead the Avengers in their time - traveling adventures.
Hisoka is extremely popular in fanfiction. His unpredictable and somewhat insane nature makes for great plot - driving elements. Fanfictions might explore his motives more deeply or put him in situations where he has to interact with the main characters in unexpected ways. Additionally, characters like Illumi also gain popularity as his complex relationship with Killua can be explored in many different and fascinating ways in fan - created stories.
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.
The idea of changing the Hunter x Hunter world's history is also fascinating. In a time travel fanfic, a character could go back in time and prevent certain events from happening, like the Chimera Ant invasion. This would completely change the world's political and power structure, and we could see how the characters adapt to this new, alternate reality.
Gon Freecss is really interesting. He's a determined and kind - hearted boy with a strong sense of justice. His journey from a simple boy to a powerful Hunter is captivating.
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.
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.