One idea could be that the 'daddy' figure in the supernatural world has to protect his child from an ancient evil that has awakened. Maybe the child has a special power that the evil wants to use for its own gain.
Well, perhaps the 'daddy' is a fallen angel in this fanfiction. He's trying to raise his half - human child in a world that is both fascinated and fearful of the child's unique supernatural abilities. He has to constantly battle other supernatural beings who either want to harm or use the child.
The main character could be a vampire daddy. He has a human daughter that he turned into a vampire at a young age to save her life. Now he has to deal with the consequences of her new existence and teach her how to survive in the vampire world.
One plot idea could be that the original female character (ofc) is a new transfer student from a different magical school. She has unique magical abilities that Harry and his friends have never seen before. This leads to a series of adventures where they try to understand her powers and how they can be used against the dark forces. Another idea is that the ofc is a descendant of an ancient magical family that has been in hiding, and she brings knowledge of long - lost spells and artifacts to help Harry in his fight against Voldemort.
One idea could be that Damon is chloroformed by an enemy in the fanfiction. This could lead to a situation where his friends have to search for him and rescue him. It might also be used as a way to incapacitate him temporarily while some secrets are revealed or a plot against him is set in motion.
One plot idea could be that the sister, after being drugged, has some sort of psychic connection with the vampires in The Vampire Diaries world. Maybe she can see their memories or feel their emotions, which leads to a series of adventures where she tries to use this new - found connection to help or hinder the vampires' actions.
Perhaps in a fantasy world, a rich lord takes Merlin as his 'sugar baby' not realizing Merlin's true potential as a powerful wizard. As time goes on, Merlin uses his influence over the lord to bring about positive changes in the kingdom, like improving the living conditions of the poor. This could lead to a complex relationship where the lord slowly discovers Merlin's magic and they have to deal with the consequences.
One plot idea could be Ketch getting involved in a time - travel adventure within the Supernatural universe. He could go back in time and interact with the Winchester brothers at different points in their lives, changing the course of events in unexpected ways.
One plot idea could be that the Winchester brothers have to face a water - dwelling supernatural creature while on a boating trip. Maybe it's a mermaid - like being that lures sailors to their doom, and they have to figure out how to stop it without getting trapped in its watery lair.
One idea could be a character reincarnating as a powerful supernatural being in a different era and having to adapt to new powers and a new world order. For example, a modern - day human reincarnates as a vampire in the Victorian era and has to deal with the strict vampire society rules while also trying to figure out their new vampiric abilities.
One idea could be that Mjolnir has a connection to an ancient supernatural being in the Supernatural universe. For example, it might be the key to sealing away a powerful demon that was once imprisoned by the Norse gods. The Winchester brothers could find out about this connection and have to protect Mjolnir from various creatures who want to use it for their own evil purposes.
Another plot could involve a Pokemon with psychic powers so strong that it can create entire alternate realities. Trainers get trapped in these realities and have to figure out how to escape while also dealing with the strange Pokemon that exist there. This could involve a lot of exploration and mystery-solving.