A plot could involve Demetri being magically bound to Harry for a short period. During this time, they have to learn to work together despite their different allegiances. Demetri could teach Harry some of the more advanced dark magic defenses that the Death Eaters use, while Harry could show Demetri the power of friendship and loyalty. This could lead to a complex relationship between them and an interesting story of redemption for Demetri.
One idea could be Demetri getting caught in the middle of a Hogwarts mystery. Maybe he's sent on a mission by the Death Eaters that somehow intersects with Harry's search for a Horcrux. Another could be a story where Demetri has a change of heart and decides to help Harry, seeing the error of Voldemort's ways.
Maybe in a fanfiction, Demetri discovers that Bella has a hidden power that not even the Cullens are aware of. He then has to decide whether to report it to the Volturi or keep it a secret and help her develop this power. This could create a complex relationship between them, full of trust issues and moral dilemmas.
One idea could be Demetri and Leah teaming up to protect the Forks area from a new threat that neither the vampires nor the werewolves have faced before. They might start off as reluctant allies but gradually develop respect for each other.
One idea could be a story where Demetri and Heidi are sent on a secret mission by the Volturi. They have to infiltrate a group of rogue vampires who are causing chaos in a small town. Along the way, they start to question their loyalty to the Volturi as they see the good in the town's people.
One idea could be that Jane and Demetri are sent on a secret mission by the Volturi. They have to infiltrate a group of vampires who are suspected of planning an uprising against the Volturi. Along the way, they start to question their loyalty to the Volturi as they see the other vampires' reasons for wanting change.
A great plot for a Potter Manor fanfiction could involve a mystery that surrounds the manor. For instance, strange noises at night lead Harry to uncover a long - forgotten chamber. It could also be about Harry restoring the manor to its former glory, perhaps with the help of Hermione's research on ancient magic used in the construction of such manors.
One interesting plot idea could be exploring what would happen if Harry had a different upbringing, like being raised by the Malfoys. It would completely change his view of the wizarding world and his relationships. Another idea might be a time - travel fanfic where Harry goes back to the Marauders' era and interacts with his parents and their friends. This could lead to him preventing certain tragedies or changing the future in unexpected ways. And then there's the concept of a fanfic where the roles are reversed, and Voldemort is the one trying to protect the wizarding world from a greater evil, with Harry being the main antagonist.
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'.
Another plot could be that a magical experiment at Hogwarts creates a portal to Starfire's world. Harry and some of his classmates end up there. Starfire has to help them get back home while also protecting her own planet from the dark wizards who have followed them through the portal.
One idea could be being reborn as Harry's long - lost twin. You could then have a whole new dynamic where you both share the burden of being the Boy Who Lived, but also have your own unique abilities and personalities. Another plot could be being reborn as a Slytherin who tries to change the house's reputation from the inside. You might start off being shunned by the other Gryffindors and friends of Harry, but slowly prove that not all Slytherins are bad.
Maybe a story where Harry Potter himself is revealed to be an Immortal. He would have to balance his fight against Voldemort with the rules of the Highlander's world. This could add a whole new layer of complexity to his journey. He might learn new combat skills from the Highlander lore and use them against Death Eaters.