One idea could be that the OC is a new vampire in town and Mitchell takes it upon himself to mentor the OC. They could get into all sorts of adventures, like dealing with vampire hunters together.
The OC could be a witch who accidentally casts a spell on Mitchell. This leads to a series of comical and dangerous situations as they try to reverse the spell while also getting to know each other better and forming an unlikely friendship.
Maybe the OC is a werewolf who has a strange connection with Mitchell. Their relationship could be explored as they both try to navigate the challenges of being non - human in a human world. For example, they might team up to protect a group of humans from a common enemy.
One idea could be an OC human who discovers a hidden power within themselves that can interact with the Cybertronian technology in unique ways. For example, they might be able to heal damaged Transformers using a strange energy they possess. Another plot could involve an OC human getting caught in the middle of a battle between the Autobots and Decepticons and having to use their wits and new - found friendships with the Autobots to survive and help them. A third idea is an OC human who is a mechanic and accidentally creates a new device that attracts the attention of both Autobots and Decepticons, leading to a series of adventures as they try to keep it out of the wrong hands.
An OC who is a human detective investigating strange occurrences in the 'Highschool DxD' world. They could end up forming an unlikely alliance with the devils. This would bring a new perspective as they try to understand the complex relationships and power dynamics in the series.
One plot idea could be that Naruto is a celestial being sent to the human world on a mission. He has powers far beyond what normal ninjas possess, like the ability to control the elements on a much larger scale. For example, he could stop a natural disaster by simply willing it. Another idea is that he's a spirit in a human form, and he has to find a way to return to his spirit realm while still protecting the village. This could involve him learning about his true identity through a series of mysterious encounters.
One idea could be that Josh and Nora travel to a new town where they discover a hidden community of other supernatural beings. They have to decide whether to join this community or keep their distance. Another could be that Nora gets a job at a hospital where she has to deal with a co - worker who is secretly investigating her and Josh's strange behavior. A third idea is that they plan a trip to a place from Nora's human past, and along the way, they face various challenges that test their relationship.
A more complex plot could be that there is a powerful ancient curse that starts to affect all supernaturals in the area. Aiden and Josh have to team up with other 'Being Human' characters to find the origin of the curse and break it. They would face many obstacles along the way, including internal conflicts within the group due to different species' instincts.
One plot idea could be the challenges she faces in hiding her pregnancy from certain characters in the fanfic's world. Maybe there are those who would use it against her or the group she's associated with.
One common theme is the struggle between Mitchell's vampire nature and his human side. Writers often explore how he tries to reconcile the two, like in 'The Battle Within Mitchell' where he constantly fights his bloodlust while trying to live a normal life among humans.
A good plot could involve a human OC who is a doctor. They end up treating a ghoul who was severely injured in a fight. This starts a strange relationship where they try to understand the nature of ghouls better. As they get more involved, they learn about a secret organization within the ghoul world that is planning something big that could endanger all of Tokyo. The OC then has to decide whether to stay out of it or try to stop it. It's a plot full of moral dilemmas and action. Also, a plot where the human OC is an artist and they use their art to show the hidden side of the ghoul - human relationship could be interesting. Their art could either be a way to promote peace or it could stir up more trouble depending on how different groups react to it.
One plot idea could be that the OC is initially scared to tell Itachi about the pregnancy. She might worry about how it will affect his mission or his standing in the ninja world. Another could be that Itachi, being the protective type, goes to great lengths to keep the OC and the unborn child safe from his enemies. He might even consider leaving his organization to ensure their safety.
One plot idea could be the OC struggling with the idea of being a mother at a young age while Sasuke is away on a mission. She has to deal with the judgment of the village and her own insecurities. Another could be Sasuke's reaction when he finds out. He might be initially shocked but then become very protective.