To write an interesting plot for Highschool DxD OC fanfiction, first, create a goal for your OC. This could be something like winning a tournament or uncovering a hidden truth. Then, build obstacles in their way. These obstacles can be other characters, difficult tasks, or even their own insecurities. You can also introduce new concepts or ideas that are related to the Highschool DxD universe but haven't been explored much. This will make your plot fresh and engaging. Additionally, make sure to have a good pacing. Don't rush through important events or drag out the unimportant ones.
One tip is to start with a conflict. It could be an internal conflict within your OC, like struggling with their newfound powers. Or it could be an external conflict, such as a new enemy threatening the peace between the devils, angels, and fallen angels. Another thing is to incorporate the existing Highschool DxD lore. This gives your fanfiction a sense of authenticity. For example, use the different rankings of devils and angels in your plot.
When writing a believable male OC for a Highschool DxD fanfic, consider his flaws. No one is perfect. Maybe he's a bit clumsy or has a short temper. These flaws make him more human. His relationships also play a big role. How he interacts with the other characters in the Highschool DxD universe should be based on his personality. For instance, if he's an introvert, he might be hesitant to join social events. And his goals and dreams should be clear. Whether it's getting better grades, impressing a girl, or becoming a stronger fighter, it gives direction to his character.
A plot could involve the mute OC being a new transfer student in the school. Their muteness makes them an object of curiosity and some characters might initially misjudge them.
Another plot could involve the OC being sent by an unknown force to either help or hinder Lucifer. They initially seem like an enemy but as the story progresses, it's revealed that they are actually on the same side. They could team up to fight against a common threat to the devil world, like an ancient evil that is starting to rise again.
One idea could be an OC demigod who has the power of a forgotten god. They could use this power to help the main characters in unexpected ways, like having the ability to manipulate time on a small scale during battles. Another plot could involve the OC demigod trying to find their place in the world of Highschool DxD, being half - god and half - something else. They might struggle with acceptance from both the devil and angel factions.
One idea could be an OC who is a gamer and discovers a hidden power within the Highschool DxD universe while playing a virtual reality game related to it. This power could be something unique like the ability to control shadows in the DxD world.
One idea could be an OC who is a hybrid of a devil and a fallen angel. The story could revolve around their struggle to find a place in both worlds. They might face discrimination from pure - blooded devils and fallen angels alike, but also discover unique powers that come with their hybrid nature.
One interesting plot idea could be an OC with a Sharingan who transfers to the Highschool Dxd world. They could use their Sharingan abilities to detect the devils' true forms and powers. For example, during a Rating Game, the OC could analyze the opponents' strategies in an instant using the Sharingan's precognitive abilities.
One idea could be a Neko OC who has a unique power, like the ability to control shadows. She could use this power to protect the main characters in secret, and as the story progresses, she gradually reveals herself and her motives. Another plot could involve a Neko OC from a different dimension who gets lost in the Highschool DxD world and has to find a way back while getting involved in the local supernatural affairs. Maybe she forms an unexpected alliance with a group of devils or angels.
One idea could be an OC who is an exorcist with a special power to see the true forms of devils. They could start off as an enemy to the devils in the Highschool DxD world but then gradually form alliances due to a common threat. For example, a new, more powerful and evil force emerges that targets both exorcists and devils.
Well, another plot could be that the OC is an old friend of Sona from a different dimension. They are reunited in the High School DxD world. The OC has a special ability to see the future in fragments. Using this ability, they start to foresee some dangerous events that could endanger not only Sona but the entire school. So, they work together to prevent these disasters. This could involve a lot of strategy and some cool battles against various foes.