Lucifer in this fanfiction could be depicted as a complex character. He's likely to be extremely powerful, with a commanding presence. His intelligence would be sharp, always strategizing and thinking several steps ahead.
The OC could have a unique appearance, like having heterochromatic eyes, one gold like Lucifer's and one a deep purple. Their hair could be a color not seen often in the series, such as silver. And they could have a special mark on their body that is related to their power or connection to Lucifer.
A fanfiction idea could be that Lucifer from the Highschool DxD universe somehow ends up in the Naruto world. In the Naruto world, he could be seen as a powerful and mysterious figure. He might interact with the ninja clans and shinobi, and his powers could be both feared and respected. He could also have some kind of connection with the tailed beasts or the Sage of Six Paths. The story could revolve around how his presence disrupts or changes the balance of power in the Naruto world.
One popular type of fanfiction about Vali Lucifer in Highschool DxD could be his power development. Writers might explore how he further hones his abilities, perhaps by training in new, secret locations. This could involve him facing off against powerful, previously unknown foes that push his limits and force him to unlock new levels of his power.
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.
A lot of these fanfictions also deal with relationships. Lucifer's relationships with the other characters in the Highschool DxD universe, such as Issei or Rias, are explored. It could be a mentor - mentee relationship, a friendship, or even a more complex romantic relationship in some cases. And there's also the theme of mystery. Lucifer has a lot of secrets, and fanfictions often delve into uncovering those secrets and what they mean for the overall story.
Often, they feature Issei with enhanced powers due to his Lucifer connection. This can lead to more epic battles and power - up moments. The stories may also delve deeper into the lore of the devil world, exploring things that the original series only hinted at.
Yes, there are quite a few. You can find some on fanfiction.net. Just search for 'Highschool DxD Issei Lucifer' and you'll get a list of stories. Some of them might focus on Issei's growth as a devil with his Lucifer powers, while others could be about his relationships in a more in - depth way.
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.
Friendship and rivalry are also common themes. Characters from Naruto and Highschool DxD may form new friendships or become rivals. For example, Naruto's friendly and outgoing nature might lead him to make friends with some of the characters in Highschool DxD, but his power also might make others see him as a rival. And in some fanfictions, the Lucifer aspect might add an extra layer of mystery or power dynamic to these relationships.