Rias could be a main character. She has a strong connection with Issei and in a fanfiction about him as the Prince of Darkness, she might play a role in helping him control his new power or deal with the political ramifications of his new status.
Grayfia could be a character that interacts with Issei. She has a lot of knowledge about the underworld and could be guiding Issei in matters related to his new position. Maybe she helps him understand the complex politics and power structures in the world of the Prince of Darkness. Also, Xenovia could be there, as she is a strong fighter. She might team up with Issei in battles and have some interesting conversations about his new identity and what it means for their cause.
Akeno could also be important. Given her own powers and her relationship with Issei, she could be involved in battles alongside him or be a source of comfort and advice as he navigates his new role. There could be some really interesting scenes between them, like when she helps him understand the darker aspects of his power. Another character could be Vali. Vali is a powerful rival and in this fanfiction, he could either be an enemy trying to overthrow Issei as the Prince of Darkness or an uneasy ally in the face of a greater threat.
Sadly, I have no idea who the author of 'issei is the darkness fanfiction' is. Fanfiction can be created by many different people all over the world, and without more context or research, it's impossible to determine the author.
Obviously, the oc reborn as Issei would interact with Rias Gremory. She is a central character in the High School DxD world and as Issei is part of her peerage, the oc in Issei's place would have a lot of interaction with her. This could range from her guiding the oc in the ways of the devils to them having some sort of romantic or at least a very close friendship relationship.
In many Issei in the Darkness fanfictions, Issei often undergoes character development. He might face new challenges that are different from the original story. For example, his relationships with other characters can be re - defined. He could form stronger bonds with some characters while having more complex rivalries with others. This makes the fanfiction interesting as it gives a fresh perspective on the character.
Since it's a fanfiction about Issei and 'the darkness', it might be a story that delves into the darker aspects of Issei's character. It could be set in a world where 'the darkness' is a powerful and menacing presence. Issei could be on a journey to either embrace or overcome this 'darkness'. There could be other characters involved who either help or hinder him in this exploration of the 'darkness' within and around him.
Well, Issei is of course the main character. There may also be other characters like his in - game friends or teammates. Maybe there's a mentor - like figure who helps him improve his gaming skills.
The character of Issei already has a large fan base from the original work. When combined with the concept of the Darkness, it allows for crossovers and mash - ups with other concepts or characters that fans might be interested in. For example, there could be a story where Issei in the Darkness encounters a character from another popular series, creating a whole new dynamic.
One plot idea could be Issei facing a powerful new enemy that challenges his status as the Prince of Darkness. He might have to gather allies from different realms and use his unique powers in new ways.
Issei is the central figure in 'badass issei fanfic'. But there are other characters too. For example, the villains he faces. They are designed to test his new - found badass skills. And then there are his comrades from his group who interact with him in different ways, depending on how his badass personality affects the group dynamics.
It could be an old enemy of the group who has a personal vendetta against Issei. This antagonist might be jealous of Issei's power or popularity within the group and plots to turn everyone against him. They could spread false rumors or create false evidence to make it seem like Issei has betrayed the group.
A group of vampire hunters could also be the antagonists. They might not be able to tell the difference between Issei and a full - blooded vampire and target him. They could be very zealous in their mission to wipe out all vampires and view Issei as just another one to be hunted down.