There's a fanfic called 'Hisoka's Obsession with Machi'. It delves into Hisoka's perspective. He is constantly intrigued by Machi's skills and her cold exterior. The story has some interesting scenes where Hisoka tries to get closer to Machi, and Machi is both repelled and fascinated by him at the same time. It's a really engaging read.
Another theme is the idea of an unorthodox relationship. They are both rather strange characters in their own ways, and fanfics usually show how their relationship is not like a normal friendship or romance. It's something much more complex and full of intrigue.
Themes are important too. In a Hisoka x Machi fanfic, themes like love - hate relationships, power dynamics, or self - discovery can be explored. For instance, Machi might discover a new side of herself through her interactions with Hisoka. And the fanfic should be well - written in terms of grammar and style, so that the reader can fully immerse themselves in the world of Hunter x Hunter and the relationship between Hisoka and Machi.
The plot could also involve her having unique nen abilities different from Hisoka's. She might be on a journey to understand these powers and in the process, cross paths with the main characters from Hunter x Hunter. Perhaps she forms an unlikely alliance with Gon and Killua, who initially are wary of her because of her relation to Hisoka, but later come to respect her for her own qualities.
Fanfiction.net is also a popular place. There are numerous Hunter x Hunter fanfictions there. However, the tagging system might not be as refined as AO3. So you may need to do a bit more digging. Look for stories with high reviews and ratings as they are more likely to be well - written and relevant to what you're looking for.
One great Hisoka - centered fanfiction might be those that explore his complex relationship with other characters in a more in - depth way. For example, a story could focus on his interactions with Gon and Killua from a more mature psychological perspective. It might show how Hisoka views their growth and potential as opponents or something more nuanced in his mind.
There's 'The Unlikely Alliance'. In this fanfic, Hisoka and Illumi find themselves in a situation where they have to work together. It shows their initial distrust but also how they gradually come to understand each other's strengths and weaknesses, which is really interesting to read.
Her character could start off as innocent, unaware of her father's dark side. As she grows and experiences more of the world of Hunters, she becomes more complex. For instance, she might witness some of Hisoka's cruel acts and be conflicted between her love for him as a father and her moral compass.
You can try searching on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They usually have a large collection of fan - created works. Just type in relevant keywords like 'Hisoka x Harry Hunter x Hunter' in their search bars.