Power - building is a common theme. The OC usually starts off with some sort of special ability or knowledge and uses it to gain more power in the Highschool DxD universe. This power - building often attracts the attention of various female characters, leading to the formation of the harem.
There's also 'Rising of the OC in DxD'. In this fanfiction, the OC is a reincarnated being. He uses his past - life knowledge to his advantage in the world of Highschool DxD. His harem includes characters from different factions, and the story delves into how he manages to keep them all together while facing various challenges from the supernatural world.
The OC can stand out by having a distinct personality. For example, if all the other harem members are bold and outgoing, the OC could be more reserved and intellectual. This contrast would make them interesting. Also, a unique skill or ability, like being able to communicate with spirits, would set them apart.
You might want to check out 'The Lone Knight in Highschool DxD'. The OC in this story really dislikes the harem aspect and has some interesting interactions because of it.
Well, you might want to check out 'The Lone Warrior in Highschool DxD'. The OC in this one really dislikes the harem concept and it's got some interesting plot twists.
The OC can stand out by having a distinct personality. For example, if most of the harem members are more on the outgoing and aggressive side, the OC could be calm and collected. Their different approach to situations would make them noticeable. Also, having a unique power or ability that no one else in the harem has would definitely set them apart.
One idea could be the OC having a unique power that attracts the various characters in the harem. For example, if the OC can manipulate time in a certain way, it could lead to some really interesting situations. Maybe they use this power to save a member of the harem from a dangerous situation, which then makes that character develop strong feelings for the OC. Another plot idea is the OC being from a different dimension and having to adapt to the Highschool DxD world while building relationships with the harem members.
An OC could stand out by having a special skill or talent. Maybe the OC is an amazing cook and can make the most delicious food. In a world where battles and magic are common, this simple yet appealing talent could draw in characters from the series. They would be intrigued by this different side of the OC and gradually form a harem around them. It also gives a chance for some cute and comical interactions, like when the characters are all eagerly waiting for the OC's next meal.
One idea could be that the OC has a unique power that helps Rias and her harem in unexpected ways. For example, the OC might be able to sense danger before it arrives, allowing them to better prepare for battles against other factions. Another plot could involve the OC having a past connection to one of the members of Rias' harem, which creates some drama and tension as they navigate their new relationships within the harem. Maybe the OC is a long - lost relative or an old friend who has changed a great deal.
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.