Simon Lewis is often a popular character. Since he has a unique background as a vampire who was once a mundane, his perspective and experiences add a lot of depth to fanfiction stories set in the Shadowhunter Academy. He can interact with the students in interesting ways, sharing his knowledge of both the mundane and the Shadowhunter worlds.
There could also be a storyline where the academy is under threat from an outside force, like a group of demons that are specifically targeting the young Shadowhunters in training. The students then have to band together, using their unique skills and the knowledge they've gained at the academy to fend off the attack. This would show their growth and development as future protectors of the Shadowhunter world.
Stiles is a must - have main character. Then, depending on the direction of the fanfiction, characters like Simon Lewis could be important. Since Simon is a vampire in the Shadowhunter universe, his interactions with Stiles, who is new to this world, could be really interesting. Also, characters like Luke Garroway, the werewolf, might play a role, especially if the story involves the relationships between different Downworlder groups and Stiles' place in all of that.
I haven't read Bella's Shadowhunter fanfiction specifically, but in general, fanfictions can be really good. They allow fans to express their love for the original work in their own way. If Bella is skilled at writing, she could have added her own unique spin to the Shadowhunter universe, perhaps delving deeper into the backstories of some characters or exploring different magical aspects.
One popular one could be 'Stiles in the Shadow World' where Stiles discovers his Shadowhunter abilities and has to navigate the complex world of Downworlders and the Clave. It has great character development and interesting plot twists.
One idea could be a crossover with the Vampire Diaries. Shadowhunters could team up with the Mystic Falls gang to fight a common supernatural threat, like an ancient demon that neither group can handle alone. This would bring together the different mythologies of the two shows.
Well, one way it could work is by having Hermione's love for knowledge translate into an interest in the Shadowhunter world. Maybe she stumbles upon some Shadowhunter lore in the Hogwarts library. Since she's always eager to learn, she becomes a huge fan. She could start comparing the magic in the Shadowhunter universe with that of the wizarding world, like how their runes are different from spells.
One idea could be exploring the backstories of minor characters in the Shadowhunter Chronicles. For example, you could write about how a particular Silent Brother came to be. Another idea is to create an alternate universe where the Shadowhunters have different powers or abilities. You could also write a fanfiction focusing on a romantic relationship that was only hinted at in the original series.
Yes, there are quite a few. You can start by looking on fanfiction websites like Archive of Our Own. There are many talented writers who have explored the concept of Bella Swan in the Shadowhunter universe. Some might focus on her having the abilities of a Shadowhunter, or her interactions with the existing Shadowhunter characters.
Yes, it can be. Since both Percy Jackson and the Shadowhunter series have large followings, the idea of combining them in fanfiction can attract a lot of attention. Fans often like to cross over different fictional universes to create new and exciting stories.