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, as the Son of Sparda, could fit in by being a new and powerful entity. He might be initially seen as an outsider, but his powers would quickly draw attention. He could become involved in the power struggles between the different factions in Highschool DxD. For example, the devils might try to recruit him, while the angels might be wary of his presence. His unique abilities would also make him a valuable ally or a fearsome opponent. And in the high school setting, he could be a bit of an enigma to the other students, both human and supernatural.
The OC's backstory as a gamer is crucial. Maybe they were a bullied gamer in the human world but in the Highschool DxD world, they find a new sense of purpose and power. Their journey from being an underdog gamer to a powerful figure in the DxD world can be very memorable. Also, give them some quirks like always quoting game lines at inappropriate times which adds humor and memorability.
One great fanfiction could be where the OC has a unique power that Akeno is initially intrigued by. For example, the OC might have the ability to control light in a different way than the devils in the Highschool DxD universe. This could lead to a series of adventures where Akeno and the OC team up to face various challenges. They could start off as just acquaintances but gradually develop a deeper bond as they fight side by side.
First, give your OC a clear backstory related to the Sharingan. Maybe they got it from a mysterious ancestor or an encounter with a powerful ninja - like being. Second, define their personality traits. For example, if they are a bit of an outcast because of their Sharingan, they could be shy but also determined to prove themselves. Third, think about their goals in the Highschool Dxd world. Are they there to master their Sharingan powers? Or are they looking for a way to go back to their own world?
First, give your Neko OC a distinct personality. For example, she could be really shy but have a hidden feisty side that only comes out when she's protecting her friends. Second, give her unique physical features. Maybe she has heterochromatic eyes, one blue and one green, which is rare among Nekos. Also, a special ability like super speed or the power to heal others quickly can make her stand out. And don't forget to give her a backstory that ties into the Highschool DxD universe, like she was an experiment by a rogue devil scientist.
First, decide on the type of youkai your OC will be. Each type has its own characteristics. For example, if it's a tanuki, it could be mischievous and good at shape - shifting. Then, think about their backstory. What led them to the world of Highschool DxD? Maybe they were drawn there by the strange energy or a quest for power. Also, consider their goals and motivations. Are they there to cause trouble, or do they have a noble purpose like protecting the weak?
To create a compelling OC, consider their abilities in relation to Excalibur. Maybe they have a special power that only activates when they are in close proximity to the sword. Or they can communicate with the spirit of Excalibur. Their appearance should also be unique. It could be a mix of modern and medieval styles, like wearing a school uniform with a knight's cape. This visual aspect will make them stand out.
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 great Highschool DxD OC Sitri fanfiction is 'The Sitri's New Ally'. It has an interesting plot where the OC, a Sitri, forms unexpected alliances within the school's supernatural hierarchy. The character development is well - done, and it keeps you engaged throughout.