In Twilight, Edward and Bella are often popular. Their complex relationship can be further explored or twisted in fanfiction. In the Shadowhunters world, Jace is a very popular choice. His brooding nature and his skills as a Shadowhunter make him an interesting character to write about.
A fanfiction could explore the idea of a character from Twilight becoming a Shadowhunter. For example, Bella could discover she has Shadowhunter blood and has to leave the vampire - werewolf drama behind to learn a whole new set of skills and rules in the Shadowhunter world. It would be interesting to see how she adapts and how her relationships with Edward and Jacob change as a result.
A plot could involve a Twilight vampire falling in love with a shadowhunter. The vampire has to deal with the shadowhunter world's rules about the supernatural, and the shadowhunter has to come to terms with loving a vampire, which goes against their training. This could lead to a lot of internal and external conflicts as they try to be together.
I think Clary from Shadowhunters would be really interesting. She's a strong - willed and powerful shadowhunter. If she were to cross paths with the Twilight characters, her inquisitive nature would lead her to try and understand their world. And her skills as a shadowhunter could be put to the test when dealing with the vampires and werewolves in Twilight.
Love and relationships are also a big theme. When different universes collide in these crossovers, new love interests can be formed. It might be between a Shadowhunter and a character from another world, and this creates all kinds of drama and tension. It's not just about romantic love, but also friendship and loyalty among characters from different backgrounds. Another common theme is the fight against a common evil. Characters from different worlds might have to team up to defeat a powerful foe that threatens both of their universes.
I really like 'Mixed Realms of Blood and Magic'. This fanfiction takes the best of Vampire Academy's vampire lore and Shadowhunters' angel - demon magic system. It has a great protagonist who is trying to find her place in this combined world of vampires and shadowhunters. There are some really intense fight scenes and lots of character development throughout.
Popular malec shadowhunters fanfiction often focuses on the intense emotional connection between Alec and Magnus. It dives into their love story, highlighting their differences and how they complement each other. For example, many fics explore how Magnus' centuries - old experience contrasts with Alec's more sheltered shadowhunter upbringing, creating a rich dynamic.
In many Shadowhunters fanfictions where Alec gets hurt, it often leads to some really emotional moments. One common scenario is when he gets injured during a fight with demons. His friends and especially Magnus might be beside themselves with worry. They would do everything they could to heal him, and this could lead to some really touching interactions between the characters, like Magnus using his magic in a very desperate way to save Alec.
Archive of Our Own (AO3) is a great platform. It has a vast collection of Shadowhunters fanfiction. There are many different genres and styles to choose from, and it's free to access. Another option could be FanFiction.net. It has been around for a long time and also hosts a large number of Shadowhunters - related fanfictions.
Love is a very common theme. Since Clace is a couple, their relationship and the challenges it faces are often explored. Another theme is adventure. They are Shadowhunters, so they often go on quests and fight against demons.