Maybe the reader has a special ability that Hisoka wants to use for his own gain. But as they interact more, he starts to develop real feelings for the reader, which creates an internal conflict for him between his self - interest and his new - found emotions.
Another interesting plot could be that the reader is from a different dimension and somehow gets trapped in the 'Hunter x Hunter' world. Hisoka is intrigued by this strange new being and they form an unlikely alliance. As they journey together, they face various challenges that test their relationship and force them to understand each other better.
One plot idea could be the reader being a new hunter who catches Hisoka's attention during the Hunter Exam. Hisoka decides to 'mentor' the reader in his own twisted way, leading to a series of dangerous and exciting adventures.
One interesting plot could be Hisoka becoming overly possessive when the reader starts getting close to another character. He might start to eliminate any potential threats in a very Hisoka - like, unpredictable way.
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 interesting aspect is the exploration of Hisoka's character. Since he is such a complex and somewhat menacing character in the original work, seeing how he interacts with an ordinary 'reader' character in fanfics can be really fascinating. For example, in some fanfics, his possessive nature towards the reader is explored in different ways, like how he protects the reader from other threats in his own unique way.
A plot could involve the reader being a healer of sorts. Flowey, being curious, approaches the reader. As they interact, the reader starts to show Flowey kindness that he's not used to. This kindness begins to thaw his cold, calculating nature. They could then go on adventures together in the Underground, with Flowey slowly becoming more protective of the reader. Also, the reader could introduce Flowey to new concepts like friendship and self - sacrifice, which would be a huge change for him.
One plot idea could be that the reader is a new ninja in the village and Sasuke is assigned to train them. Through the training sessions, they start to understand each other better and develop feelings. Another could be that the reader has a special power that Sasuke needs to help him in his quest for revenge, and as they work together, love blossoms.
One idea could be that the reader is a new resident in the haunted house where Beetlejuice lurks. They accidentally summon him while trying to fix up the old place. Another could be that the reader is a medium who can see Beetlejuice clearly and they form an unlikely friendship. Maybe the reader is a lost soul like Beetlejuice and they find common ground in their otherworldly existence.
Another plot could be that the reader is a journalist investigating the strange disappearances around an old, abandoned studio rumored to be haunted by Bendy. As the reader delves deeper, they encounter Bendy and instead of being afraid, they start to see the misunderstood side of him. This leads to a relationship where the reader tries to tell Bendy's story to the outside world and protect him from those who would do him harm.
Well, a plot could involve the reader being a bit of a troublemaker in the village. But Krampus, rather than just coming to punish, he wants to reform the reader. He takes the reader on a journey through the shadowy parts of the forest, showing the reader the spirits of those who were truly bad. This makes the reader realize their own actions are not as bad as they thought and they start to change for the better. Also, the reader could be an artist who tries to capture Krampus' essence in a painting, and this draws Krampus to the reader in a curious way.
Another interesting plot could be that the reader is a time - traveler from the future. They come to Arendelle during Elsa's reign and know about all the events that are going to happen. The reader tries to help Elsa avoid some of the hardships she will face in the future, but in doing so, they accidentally change the course of history. This creates a complex situation where Elsa and the reader have to work together to set things right while also dealing with their growing feelings for each other.
One idea could be the reader is a scientist tasked with studying SCP 682. The reader tries to find a way to communicate with it in a non - violent way. At first, SCP 682 is hostile, but gradually, through the reader's persistent efforts, it starts to show a bit of curiosity towards the reader.