One idea could be that Harry, as a demon, has to navigate the wizarding world while hiding his true nature from his friends. He might struggle with newfound powers and the urge to use them in ways that are against the wizarding code. Another plot could involve Harry being sent on a quest by the demon world to retrieve a powerful magical artifact from Hogwarts, creating a conflict between his loyalty to the wizarding world and his new demonic obligations.
Perhaps Harry, as a demon, discovers that he has a connection to an ancient and powerful demon lineage that has ties to the founding of Hogwarts. This could lead to a plot where he uncovers long - lost secrets about the school and the wizarding world. He might have to battle against other demons who want to use these secrets for their own evil purposes. Meanwhile, his friends from Hogwarts are trying to save him from his demon self, not realizing that he is actually trying to protect them and the entire wizarding world from a much greater threat that only he, with his new demonic knowledge, can understand.
One idea could be Castiel getting transported to the Harry Potter world. Maybe he tries to understand the magic there using his angelic knowledge. Another plot could involve Castiel teaming up with Harry Potter to fight a common dark force that is threatening both the wizarding world and the Supernatural world.
Perhaps the Demon Prince is actually a long - lost relative of one of the main characters in Harry Potter. This could lead to a complex web of relationships and power struggles within the wizarding world. For example, he might be trying to claim a rightful place in Hogwarts or in the wizarding hierarchy, which would put him at odds with many established characters.
One idea could be that the demon butler is secretly protecting Harry from a new, unknown dark force in Hogwarts. He uses his demonic powers to sense danger before it arrives.
A fanfiction could revolve around a powerful demon who has been trapped in the wizarding world for centuries. Harry Potter and his friends come across this demon and find out that it holds the key to defeating a new, even greater dark force that is threatening both the wizarding and muggle worlds.
One interesting idea could be exploring how the presence of demon blood affects a character's magic. For example, it might enhance certain dark arts abilities. Another could be the social ostracism the character with demon blood faces within the wizarding world, similar to how half - bloods are sometimes treated in the original series. Also, it might show how the character struggles to control the more primal and dangerous instincts associated with demon blood.
Perhaps the half - wolf demon has a special power that can help Harry Potter in his fight against Voldemort. For example, the demon can sense dark magic from a great distance. They meet in the Forbidden Forest and the demon offers his help to Harry in exchange for protection from the wizarding community's prejudice.
One idea could be that Harry struggles to control his demonic powers. For example, he might accidentally set things on fire when he gets angry. Another could be that he has to hide his half - demon nature from his friends at Hogwarts, constantly fearing discovery.
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 idea could be that the Demon King somehow infiltrates Hogwarts. Maybe he disguises himself as a new professor. This would lead to a lot of mystery and danger as Harry and his friends try to figure out who he really is.
One idea could be that the Winchester brothers from Supernatural end up in the wizarding world of Harry Potter. They could be on a hunt for a supernatural creature that has found a way to hide among the wizards. Another idea is for Harry Potter and his friends to encounter a case of demonic possession in Hogwarts, and they have to team up with the Supernatural crew to solve it.