One interesting plot could be a crossover where a Twilight character gets involved in an Original family feud in New Orleans. Maybe Bella, with her unique ability to resist vampire powers, somehow ends up in the middle of a power struggle between Klaus and his siblings.
A great plot idea might be the discovery of a common enemy that forces the Twilight vampires and the Originals to team up. For example, a new breed of super - vampires that are a threat to both groups. This would lead to some really interesting character interactions, like Edward and Elijah having to work together, each with their own code of honor and way of doing things.
Another plot could be a love triangle between a Twilight character, an Original, and a regular human. Imagine if Jacob, who has his own issues with vampires in the Twilight series, falls in love with a human who is also being courted by an Original vampire. This would create a lot of drama and conflict, not only between the different species but also within the relationships themselves.
A really cool plot for this crossover fanfiction could be that there is a prophecy in both the Twilight and The Originals worlds. It predicts that a certain character from each universe must join forces to save both worlds from a great evil. This could be a dark force that is slowly consuming all supernatural beings. Bella Swan could be the key in the Twilight world, and Hope Mikaelson in The Originals world. As they meet and start to work together, they face many challenges due to the different beliefs and power systems in their respective worlds. Their friends and families from both sides also get involved, creating a complex web of relationships and power struggles.
One interesting plot idea could be a crossover where Percy Jackson's demigod powers interact with the magic in The Originals. For example, his ability to control water could be used in a battle against the vampires in New Orleans. Maybe he helps the Mikaelson family during a flood caused by a powerful witch, using his water - based powers to save them and in turn they help him with some demigod - related problem he has, like finding a lost artifact.
One idea could be a love triangle between a vampire from 'The Vampire Diaries' and two characters from 'The Originals'. For example, a young vampire falls in love with Klaus but also has a deep connection with Elijah. This could create a lot of tension and drama as the two brothers have their own complex relationship. Another plot could involve a powerful vampire from 'The Vampire Diaries' coming to New Orleans and challenging the power structure that the Originals have built. This would lead to battles and political intrigue within the supernatural community.
One interesting plot idea could be a crossover where characters from 'Harry Potter' and 'The Originals' have to team up to fight a common dark magic threat. For example, Harry Potter and Klaus Mikaelson might initially be at odds due to their different views on magic use and power, but they realize they need each other's skills to defeat a powerful ancient evil that is threatening both the wizarding world and the vampire - werewolf - witch community in 'The Originals'.
Maybe the Avengers need the help of the witches from 'The Originals' to reverse a spell that an enemy has cast on Earth. Klaus and Loki could have some interesting interactions as two complex anti - heroes. The witches could use their magic to enhance the Avengers' weapons or powers in unique ways.
One idea could be that Buffy and her friends are called to New Orleans because of some strange vampire activity that seems linked to the Originals. Maybe the First Evil from Buffy's world has some connection to an ancient threat in the Originals' world, and they have to team up to stop it.
Perhaps a powerful enemy from Merlin's past resurfaces and is causing chaos in both his world and the world of the Originals. Merlin and the Mikaelson family have to work together to defeat this enemy. The Mikaelsons' cunning and physical strength combined with Merlin's magic could make for an epic battle. Along the way, there could be interesting character interactions, like Elijah being impressed by Merlin's wisdom and honor.
One idea could be that a powerful witch from 'The Originals' world accidentally opens a portal to the 'Supernatural' world. Sam and Dean Winchester are drawn through it and end up in New Orleans. There, they team up with the Mikaelson family to fight a common enemy, like an ancient and powerful demon that is causing chaos in both their worlds.
One idea could be an OC who is a powerful witch that gets caught in the middle of the Mikaelson family drama. Maybe she has a special power that could either help or hinder them in their battles. Another could be an OC vampire who was turned long ago and has a connection to the Originals' past that they don't even know about yet.
One interesting plot idea could be exploring how different characters adapt to the post - apocalyptic world in new and unexpected ways. For example, a character who was once a timid office worker becomes a fearless scavenger.