You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of fanfics across various fandoms. Just search for 'Toshiki Kai x Misaki Tokura' and you'll likely find a good number of stories. Another option is FanFiction.net, although the quality can be a bit more variable there.
One common theme is friendship development. Since they are characters from the same universe, many fanfics explore how their friendship could grow deeper over time. Another theme is adventure. Writers might create scenarios where they go on quests or face challenges together.
Well, without more information about the 'hachishakusama short story', it's hard to say exactly what it's about. However, if we assume it follows the pattern of many short stories, it could have a clear beginning, middle, and end. The beginning might introduce the concept of Hachishakusama, perhaps as a mystery. In the middle, the story could develop with characters either trying to figure out what Hachishakusama is or facing some sort of encounter with it. And the end could be a resolution, whether it's a terrifying conclusion where Hachishakusama prevails or a more positive ending where the characters manage to overcome the threat of Hachishakusama.
They often have a southern setting. For example, they might be set in a small, decaying southern town. They usually deal with dark themes like death, decay, and family secrets.
There is a fanfiction called 'When Pokemon Cry'. It's about a group of Pokemon who are hurt in a natural disaster and how they support and comfort each other during the recovery process. It shows the strong bond between Pokemon in difficult times. Another interesting one is 'Hurt and Hope', where a trainer helps his injured Growlithe regain its confidence after a brutal fight.
Another idea is that Zelda characters find themselves in the Naruto world. They could get involved in the ninja academy and learn about chakra. Maybe Zelda herself could try to master some of the ninja arts and use her magic in combination with it. This would lead to a lot of interesting interactions between the Zelda characters and the ninja students.
In typical 'DeviantArt Diaper Boy Story', the main character is the diaper - wearing boy for sure. Besides him, there could be a wise old man or woman who serves as a guide. Maybe there's a group of friends, some of whom are accepting of his diaper - wearing while others are not. These friends can add drama and conflict to the story. There could also be a villain who tries to take advantage of the boy's unique situation with the diaper.
One possible plot development is that Harry's friends initially don't recognize him when he's mistaken for a girl. This could lead to some really funny misunderstandings. They might start flirting with him, thinking he's a new girl in school. And Harry has to find a way to reveal his true identity without causing too much chaos among his friends.