To be honest, it's said to have elements of a real story. However, in the process of turning it into a film, some fictional elements could have been added to make it more compelling and entertaining.
Love and friendship are common themes. The relationship between Yuri and Hanako can be explored in terms of deep emotional bonds, whether it's a budding romantic love or a strong platonic friendship.
Well, a great Hanako x Yashiro fanfic is 'The Adventure Begins'. In this fanfic, Hanako and Yashiro embark on an adventure to solve a mystery in the school. It's filled with suspense and cute moments between them. 'The Secret Garden' is also a nice one. It shows a more private side of their relationship as they discover a hidden garden in the school grounds. And 'The Promise' is about the promises they make to each other during a difficult time.
You can start by looking on popular fanfic platforms like Archive of Our Own (AO3). Just use the search terms 'Hanako x Yashiro' and it should bring up a bunch of relevant fanfics. Another option is Fanfiction.net, though the selection might be a bit different. You can also check out some Tumblr blogs dedicated to the fandom, as they sometimes share or recommend great Hanako x Yashiro fanfics.
Well, if you're looking for 'yuri x hanako fanfic', you could also check out some blogs dedicated to the source material of these characters. Sometimes bloggers write their own fanfics or know of some great ones that haven't been widely discovered yet. You might stumble upon some hidden gems there.
I'm not familiar with the Nene Brooks story. It could be a personal story about her achievements, relationships, or a particular event in her life. Without more information, it's hard to tell what the story is about.