An OC (Original Character) in a Highschool DxD fanfiction having the Rinnegan could be an extremely powerful and unique addition. The Rinnegan, from the Naruto universe, brings a whole set of abilities like the Six Paths powers. In the context of Highschool DxD, this OC could use these powers in various ways. For example, the ability to see chakra could be translated into seeing the magical energy in the DxD world. They could use the gravitational powers of the Rinnegan to manipulate the environment during battles against devils, angels, or fallen angels. It would make for a very interesting and overpowered character in the Highschool DxD fanfiction setting.
The OC's Rinnegan in a Highschool DxD fanfiction would be extremely powerful. It could give the character abilities like seeing through illusions, which would be very useful against devils known for their trickery. The power to summon creatures from the Six Paths could also be a game - changer. It could summon powerful beings to fight alongside the OC in battles against other supernatural entities in the DxD world.
The balance can also be achieved by making the OC need to train and develop their Rinnegan powers gradually. They start with basic abilities and as the story progresses, they learn more complex and powerful ones. This way, they face challenges appropriate to their current power level at each stage of the story, and the power growth feels more natural and not overly sudden.
To create a compelling OC in Highschool DxD fanfiction, first think about their backstory. A tragic or mysterious past can add depth. For example, if your OC is an exiled devil, it gives a reason for their actions. Also, consider their powers. Make them unique but not overpowered to the point of being unbelievable. Maybe they have a special ability related to an element like shadow manipulation that ties into the DxD universe's lore.
Interaction with the existing cast. A good fanfiction will have the OC interacting meaningfully with characters like Issei, Rias, and others. This can include forming alliances, rivalries, or even romantic relationships. It adds depth to the story and shows how the OC fits into the already established world of 'Highschool DxD'. Well - written fight scenes are also important. Since the OC is overpowered, the battles should be exciting and show off their abilities in a cool way, like using their powers in creative combinations against strong opponents.
Another good place is Reddit. There are specific subreddits dedicated to Highschool DxD fanfiction. You can post a request asking for OP OC gamer fanfictions in that community. People there are often very helpful and can point you in the right direction. Some might even recommend their own favorites or works in progress.
Unique character design. If the original character (OC) has a distinct personality and backstory that fits well within the Highschool DxD universe, it can make the fanfiction stand out. For example, an OC gamer who has a special power related to gaming that also has an impact on the DxD world in an unexpected way.
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.
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.
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.