A possible plot idea is that a group of devils make a collective deal with a team of Hunters. The devils offer to enhance the Hunters' Nen abilities to an unprecedented level so that they can face a great threat that is emerging in the world. However, the catch is that the Hunters have to complete a series of cruel and immoral tasks for the devils. As the Hunters struggle with these tasks, they also have to keep their deal a secret from the rest of the Hunter community, which adds to the tension. And there could be a twist where the devils' real intention is not just to have the tasks done but to use the Hunters as pawns in a much larger and darker plan.
Well, a plot might involve a devil approaching a young and inexperienced Hunter. The devil offers the Hunter a deal to become the most powerful Hunter ever in return for the Hunter's soul after a certain period. As the Hunter rises in power, they attract the attention of other Hunters, some who suspect something is wrong. This could lead to a conflict between those who want to help the Hunter break the deal and those who see the Hunter as a threat due to their newfound and possibly dangerous power. Also, the devil could be using the Hunter to start chaos in the Hunter x Hunter world for its own mysterious reasons.
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.
One idea could be that Geru is a new type of Hunter with a unique nen ability. For example, the ability to manipulate time in a small area. This could lead to all sorts of adventures and challenges. Maybe Geru has to use this power to stop an evil group from stealing precious artifacts in the Hunter x Hunter world. Another idea is that Geru is an OC who is on a quest to find a long - lost family member who is also a Hunter. Along the way, Geru meets different characters from the original series and forms alliances or rivalries.
Another idea is a fanfic that focuses on Menchi's past. Maybe she had a mentor who taught her everything she knows about cooking and hunting for ingredients. The story could explore her relationship with this mentor, how she overcame difficulties in her training, and how those experiences shaped her into the tough examiner we see in the series.
The OC brother could have been separated from Pitou early on in their 'lives' as Chimera Ants. He grows up among humans, learning their ways and values. When he and Pitou finally reunite, they don't recognize each other at first. The story could then focus on how they gradually discover their relation and how their different experiences shape their relationship, with Pitou being more in tune with the Chimera Ant nature and the brother being more human - like in his thinking.
A plot could revolve around Menchi's past. Maybe she has a hidden connection to a powerful group or a long - lost family member. This could lead to a story of self - discovery as she uncovers secrets from her past while still maintaining her role as a hunter and a food expert. She might have to face old enemies or make difficult choices regarding her new - found knowledge.
One idea could be the main character using gamer skills to quickly learn Nen abilities in unique ways. For example, they might have a leveling system for their Nen types, which gives them an edge in battles against other Hunters or enemies.
A possible plot for 'Kaito Hunter x Hunter fanfiction' is that Kaito enters a special tournament in the Hunter x Hunter world. This tournament has rules and challenges that are different from the normal ones. He meets new and interesting characters during the tournament, some of whom become his friends and some his enemies. As he progresses through the tournament, he uncovers a conspiracy that is related to the very foundation of the Hunter x Hunter world. He then has to decide whether to expose it and risk his life or keep quiet and let the conspiracy continue.
Another plot could involve a character from the real world being transported into the Hunter x Hunter universe and having to quickly adapt to the system. They could start as a weak novice but then use their knowledge from the real world to find unique ways to level up and become a powerful Hunter. For example, they might use modern strategic thinking in battles or in exploring the complex world of Hunters.
One plot idea could be that Illumi and Hisoka are forced to team up on a mission. Their different personalities - Illumi's cold and calculating nature and Hisoka's flamboyant and unpredictable one - would create a lot of tension and interesting interactions. Maybe they have to infiltrate an enemy stronghold and they constantly bicker about the best way to do it.
One idea could be Naruto discovers a hidden realm where devil hunters operate and he has to learn their ways to save his village from a devil invasion.