Perhaps in a post - war scenario in both the 'Harry Potter' and 'Mortal Instruments' universes, Hermione and Draco decide to collaborate on a project to bridge the gap between the two magical communities. Along the way, they face opposition from traditionalists in both worlds who don't want the two communities to mix. Their relationship could develop from reluctant partners to something more as they fight for their cause. This would involve a lot of character growth, exploring new magical concepts, and dealing with the politics of both worlds.
You can start by looking on fanfiction.net. It has a large collection of fanfics related to various fandoms, including those involving characters from 'Mortal Instruments', Hermione, and Draco. Another great place is Archive of Our Own (AO3). Many talented writers post their works there, and you can easily search for crossovers or stories that combine these elements.
One idea could be a crossover with the Harry Potter universe. The Shadowhunters could visit Hogwarts and interact with the wizards. They might have to team up to fight a common dark magic threat that combines the magic from both worlds.
Perhaps Draco is falsely accused of a serious crime and is about to be sentenced to a harsh punishment in the wizarding world. Hermione, believing in his innocence, undertakes a dangerous mission to find evidence that will clear his name. She delves into old wizarding archives, faces some of Draco's old enemies who want to see him go down, and finally manages to present the evidence just in time to save Draco.
One idea could be that the Shadowhunters from The Mortal Instruments have to deal with the presence of vampires from Twilight in their world. Maybe they initially mistake the Twilight vampires for demons and chaos ensues. The Clary from The Mortal Instruments could form an unexpected alliance with Bella from Twilight to figure out how to co - exist.
One idea could be creating an OC who is a half - angel, half - demon. This would bring a unique perspective to the story as they struggle with their dual nature in the world of the Mortal Instruments. They could be on a quest to find a way to balance their two halves and in the process, interact with the main characters in unexpected ways.
In a fanfiction plot, there could be a situation where Hermione and Draco are both cursed. The only way to break the curse is to work together and learn to trust each other completely. They have to rely on each other's unique magical abilities. Along the way, they share their deepest secrets and fears, which brings them closer together. By the time they break the curse, their relationship has transformed from one of enmity to something more like friendship, with the potential for more.
A possible plot is that the boggart takes the form of a combined fear for both of them. It could be a powerful dark wizard who has enslaved the wizarding world, and only Hermione and Draco, with their combined knowledge and skills, can defeat it. As they face this boggart, they learn to trust each other more than they ever thought possible.
In some fanfictions, there could be a time - travel plot where Draco and Hermione from different timelines end up together and Hermione gets pregnant. This would involve dealing with the consequences of changing the timeline as well as their relationship dynamics.
Well, a possible plot could be that Draco and Hermione, as siblings, are both sorted into different houses at Hogwarts. They initially struggle with their loyalty to their houses while also trying to figure out their new relationship. There could also be a plot where they discover a common enemy within the wizarding world who is trying to harm their family, and they must use their combined skills to defeat this foe.
One idea could be that Draco and Hermione start a family in secret at first. Maybe they meet in a post - war setting where they both realize they have more in common than they thought. Their children could inherit a mix of their magical abilities and personalities, leading to unique family dynamics.