One idea could be that the OC is a new vampire in town. Rebekah takes an interest in them because they seem different from the other vampires she's known. They could go on adventures together, facing other supernatural threats while also exploring their growing relationship.
One idea could be that the OC is a powerful witch who gets caught in the middle of the Salvatore - Rebekah drama. She might initially befriend Rebekah, not knowing her full vampire nature, and then fall for one of the Salvatores. This creates a love triangle full of supernatural twists.
One plot idea could be an OC who is a long - lost relative of the Mikaelsons. They show up in Mystic Falls and at first, the Mikaelsons are suspicious. But as time goes on, they start to form a bond, especially Rebekah. Another could be an OC who is a powerful witch and is brought in to help the Mikaelsons with a new threat. Rebekah might initially be jealous of the OC's power but then realizes they can work together. A third idea is an OC who is a human with a special ability to see the future. Rebekah tries to use this to her advantage in the vampire - filled world she lives in.
A more complex plot could be that the OC is a time - traveler. They accidentally land in Rebekah's time period. At first, Rebekah is suspicious of the OC, but as the OC reveals knowledge of future events that could help Rebekah and her family, they form an alliance. However, changing the past has unforeseen consequences that they must deal with.
Well, you could have a plot where the OC is a healer - type with a quirk that can cure any injury or illness. However, there's a catch - using the quirk drains the OC's own life force. The BNHA characters initially doubt the OC's abilities because they seem too good to be true. As the story progresses, the OC proves their worth during a major battle where many heroes are injured. They have to decide how much of their own life they are willing to sacrifice to save others, and this creates a deep emotional and moral dilemma.
Perhaps the OC is a scientist who has been researching a new form of energy. This energy is actually what powers the Sekirei. The OC's research attracts the attention of a group of Sekirei. One Sekirei in particular befriends the OC to learn more about this energy. As they spend time together, the OC begins to understand the Sekirei's world better and helps them find a way to break free from the constraints of the Sekirei Plan.
To develop Rebekah, explore her past more. How has her time as a vampire affected her relationships? What are her hopes and dreams? For the OC, build their backstory gradually. For example, if they're a werewolf, how did they become one? How has it shaped their view of the world? Let their relationship develop organically. As they interact, they learn more about each other and change in response to each other.
You can start by giving the OC a distinct backstory. For example, if they're a vampire, explain how they were turned and what their human life was like. This will shape their personality and values.
One idea could be a story where the OC is a traveler who meets Obara in a strange land. They start off as strangers but gradually form a deep bond as they face various challenges together, like surviving in a harsh wilderness or solving the mystery of an ancient ruin.
One idea could be an OC who is a foreign ninja from a far - off land coming to Konoha. Their unique fighting style and culture shock could create interesting storylines. For example, they might introduce new jutsu techniques that the Konoha ninjas have never seen before.
One idea could be a story where Gai and the OC meet during a difficult mission. The OC is initially skeptical of Gai's flamboyant style but gradually comes to respect his skills and positive attitude. They then form an unlikely partnership and face various challenges together, growing closer as they overcome each other's weaknesses.