Well, you could do a time - travel fanfiction within the Shadowhunter Chronicles. Imagine a character going back in time to prevent a major disaster that changed the course of the Shadowhunter world. Or, write a story from the perspective of a Downworlder who has to interact with the Shadowhunters in a unique situation, like being forced to team up to fight a common enemy that is even more powerful than the usual threats they face. And of course, a story about a lost or forgotten Shadowhunter family and their journey to reclaim their place in the Shadowhunter society.
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.
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.
A possible plot is a story where a character from Harry Potter accidentally travels to the Shadowhunter world. Let's say Neville Longbottom. He could end up at the Institute and be mistaken for a mundane at first. But as he starts to show his magical abilities, the Shadowhunters realize he's from a different kind of magic. He could then share his knowledge of herbology with them, which could be useful in creating new potions or antidotes in the Shadowhunter world. In return, he could learn about their combat techniques and bring some of that knowledge back to Hogwarts.
First, re - read the books or re - watch the shows to get a good feel for the world, characters, and the rules. Then, come up with an interesting concept. It could be a new adventure for the main characters or a story about a new character you create. Next, make a basic outline of the plot, including the beginning, middle, and end. After that, start writing the first draft, don't worry too much about grammar and spelling at first.
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.
One idea could be exploring the backstory of a minor character in the Kingkiller Chronicles. For example, the life of the innkeeper before Kvothe arrived. Another idea is to create an alternate ending where Kvothe makes different choices. Maybe he decides not to seek revenge, which would lead to a completely different series of events. A third idea could be a story set in the same world but focusing on a new character's journey to become a magician in a different part of the realm.
One idea could be to explore the backstories of the minor characters. For example, what was the life of a particular servant in the lunar court before the main events of the story? Another could be to create an alternate ending where Cinder doesn't become the queen. Maybe she decides to leave the lunar world altogether and start a new life on Earth in disguise.
Well, for 'dragon chronicles fanfiction', you could write about a dragon rider who discovers a new type of magic that only certain dragons possess. This could lead to a whole new set of challenges and adventures as they try to master this magic. Or perhaps a story about a dragon that has lost its memory and is trying to figure out who it is and where it came from. Also, a fanfic could be about a group of dragons that are trying to protect a sacred place from humans who want to destroy it for resources.
One idea could be exploring the backstories of the dragons in more detail. Maybe a dragon was once a human and was cursed to become a dragon, and the fanfiction could focus on their journey to break the curse.
One idea could be to cross Nick with a popular fantasy world like Middle - earth. Nick could be a new character in that world, facing the challenges of orcs and dark magic. Another is to cross him with a superhero universe, where he has to use his unique skills among the superpowered beings. Maybe he teams up with a telekinetic hero to stop a common enemy.
One idea could be exploring the backstory of a minor character in the Underland Chronicles. Maybe a character who only had a brief appearance but has a rich history that could be developed.