Well, a plot could involve an OC who is a gamer and a big fan of Dxd. They end up in a junkyard where they accidentally open a portal to the Dxd realm. Since they are a gamer, they quickly adapt to the new world and use their gaming skills to become OP. They could start by forming alliances with different factions in the Dxd world and use their junkyard - found items as unique weapons or tools.
Here's a more detailed plot. An OC gamer is exploring a junkyard when they stumble upon a strange device. It transports them into the Dxd universe. At first, they are weak and clueless. But as they explore more, they discover that they can use their gaming knowledge to their advantage. For example, they know strategies from games that can be applied to battles in the Dxd world. They start to collect items from the junkyard that have some magical properties in the Dxd world. With time, they develop OP abilities, like being able to combine different powers or use their junkyard items in unexpected ways. This makes them a unique and powerful entity in the Dxd world, and they get involved in all sorts of adventures, from helping out in wars to solving mysteries.
To create a memorable OC, give them a unique backstory related to the junkyard. Maybe they grew up there and learned to build things from the scraps, which gives them an edge in the Dxd world. Also, their OP ability can be something that ties in with their gamer side, like being able to hack into magical systems in the Dxd world because they were good at hacking in games.
One idea could be an OC with a unique sacred gear that has powers no one has seen before. For example, a sacred gear that can manipulate time on a small scale, allowing the OC to freeze time briefly during battles in Highschool Dxd's universe. This would add a whole new dynamic to the battles and interactions.
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.
An interesting plot could be an OC gamer who is known for their role - playing skills in the human world. When they enter the Highschool DxD world, they start to role - play as a powerful being. This act fools many of the characters at first, but as time goes on, they have to actually become strong to keep up the facade and end up changing the power dynamics in the DxD world.
One idea could be an OC with a unique gaming ability that allows them to level up their magic skills faster in the DxD world. For example, they could have a 'gaming HUD' that shows hidden stats of enemies, giving them an edge in battles.
Well, you could have an OP OC who is a master of ancient magic. He could use this magic to outwit the devils, angels, and fallen angels in the DxD universe. Maybe he has a secret past that ties him to an ancient prophecy, and as he discovers more about it, he has to face powerful enemies. You can also focus on his relationships, like having a romantic interest with a character from the original series that changes the power dynamics between different factions.
One idea could be an OC who is a gamer in the High School DxD world and uses their gaming knowledge to strategize in battles. For example, they might use their understanding of RPG leveling systems to level up their own powers faster than others.
One plot idea could be an OC who is a reincarnated angel in the Highschool DxD world. The OC has to hide their true identity while trying to stop a secret group of devils from starting a war between the three factions. They could team up with Issei and his friends, but there would be constant suspicion from the devils around them.
There's a fanfiction where the op oc gamer has the power to level up like in a game. In this story, they use their unique skills to navigate the complex world of Highschool DxD, making allies and facing off against powerful foes. It's really exciting as it combines the game - like mechanics with the supernatural elements of the series.
One idea could be an OC who is a gamer in the modern world suddenly gets transported into the Fate Stay Night universe during the events of the opening sequence. They could use their gaming knowledge, like strategic thinking and quick reflexes, to survive and make an impact on the Holy Grail War.