One idea could be that the princess has a secret power that is awakened by the Twilight world. Maybe she can communicate with the Twilight creatures and they help her solve a mystery in her own kingdom.
Another plot could be that the Twilight world is in danger and the princess, with her unique human qualities, is the key to saving it. The Twilight characters initially don't trust her, but as she shows her courage and kindness, they come to rely on her.
A great plot for a Twilight Princess story fanfiction could be a time - travel aspect. Link somehow gets sent back in time to a point before the Twilight invasion. He could then try to prevent it from happening in the first place. This would involve him interacting with characters in a different way, and he might have to make some tough decisions about changing the future.
One idea could be Link and Ilia going on a secret adventure to discover a hidden magic within the Twilight Realm. Maybe they find an ancient artifact that has the power to restore a part of the Twilight Realm that was damaged. Another could be a story where Ilia gets kidnapped by an unknown enemy and Link has to go through a series of difficult trials to rescue her. He could face new and dangerous creatures along the way.
A plot could revolve around Twilight Sparkle learning some special form of magic from Princess Cadance. For example, Cadance is an expert in love - based magic, and Twilight wants to understand it better to help her friends with their relationship problems. So they have a series of lessons and adventures along the way.
One idea could be exploring the origin of the psychic powers in the twilight world. Maybe there was an ancient event that triggered it.
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.
One idea could be exploring a different origin for the vampires in the 'Twilight' universe. Maybe they are not just a natural occurrence but were created by an ancient magic gone wrong. Another could be a story where a human character has the power to control the elements and how that changes their relationship with the vampires and werewolves.
A plot could be that the Twilight vampires are mistaken for a new threat by the Avengers. So, there's a lot of misunderstanding and conflict at first. But then they realize that there is a real bad guy who is using their feud to his advantage. They then have to work together to take this villain down. Also, what if some of the Avengers become vampires or werewolves? How would that change their dynamic and abilities? For instance, if Captain America became a vampire, would his sense of justice remain the same? And how would his new powers interact with his old ones?
One interesting plot idea could be exploring the backstory of a minor character in more detail. For example, a side character who has a unique power but it was never fully explored in the original. Another could be a time - travel plot where a character goes back to change an important event in the Twilight Diaries universe. And also, a plot where characters from different factions have to team up against a new, unexpected threat.
One idea could be exploring what would happen if a new vampire with a unique power entered Forks. This new vampire could disrupt the existing relationships between the Cullens and the other characters in Twilight. For example, they might have a power that could temporarily nullify the abilities of other vampires, leading to some tense and interesting situations.
One plot idea could be exploring the backstory of the characters in the 'awoken twilight' world. Maybe there was a great war or a magical event that led to their current state. Another could be a love story between an awoken and a regular human, dealing with the challenges of their different existences.