It could also be an entirely new character introduced in the fanfiction. This character might come from a different part of the supernatural world and have their own motives and goals. With Rias out of the way as the main focus, this new character can interact with the existing characters in new and exciting ways, driving the plot forward in unexpected directions.
One potential new protagonist could be Issei's other friends or comrades. Since Rias is being bashed in this type of fanfiction, they might get more screen time and development. For example, Kiba could step up and show his leadership skills and unique abilities more.
He might react with hostility. Dark Naruto has a certain edge to him, and if he sees Rias as a threat or someone he doesn't like, he'll likely oppose her. He could use his combat skills to challenge her directly.
There could be the other members of Rias's peerage. In some fanfictions, they might be forced to choose sides between Rias and the OC. For example, Akeno might be torn between her loyalty to Rias and her growing respect for the OC's abilities.
Well, one interesting aspect could be the exploration of different character dynamics without Rias being in a central positive role. It might show how other characters develop in a new light. For example, other devils or supernatural beings could step up and show their capabilities more prominently.
Well, in such a fanfiction, Dark Naruto might use his powerful and often shadowy abilities to outwit Rias. Maybe he'd expose some of her less - than - noble actions in the Highschool DxD world. He could easily overpower her in battles, using his ninja skills and the dark powers he has. For example, his shadow clones could be used to confuse Rias and her peerage while he strikes from the shadows.
The human OC can be developed by giving them unique abilities. For instance, they could have a special power that Rias doesn't have or understand. This would make them stand out and be a threat to Rias. Another way is through their backstory. A tragic or interesting backstory can make the readers sympathize with the OC and understand their motives for bashing Rias.
One common theme could be power dynamics. Since it's a Rias - bashing fanfiction, it might explore how a human OC challenges Rias' authority or power within the Highschool DxD universe. Another theme could be the exploration of different character relationships. The human OC may interact with other characters in ways that contrast with how Rias does, leading to new and interesting story developments. It could also deal with the concept of loyalty, as the OC might sway the loyalty of characters who were previously on Rias' side.
Often, there's a theme of challenging the status quo that Rias represents. In the original, she has a certain position and set of relationships. Fanfictions might bash her to create a new narrative where the OC can break free from the typical Rias - centric storylines. For example, if Rias is seen as too controlling in the original, the fanfic could have the OC resist her authority and form new alliances or ways of doing things.
One possible plotline could be that Naruto is transported to the Highschool DxD world and immediately notices Rias's overbearing attitude. He decides to oppose her and starts to gather allies among the other students and characters who are also fed up with her ways. As a result, a power struggle ensues between Naruto and Rias.
Well, it could involve Naruto characters being thrown into the Highschool DxD universe and having some sort of conflict with Rias. Maybe Naruto's skills and values clash with Rias's actions or leadership in the story. For example, Naruto might see her as too power - hungry or not treating her underlings fairly.
One popular alternate protagonist could be Kiba Yuuto. He has his own backstory and is quite popular among fans. In Issei - bashing fanfics, he could take the lead as he is strong, noble, and has his own set of values. Another could be Akeno Himejima. She has a complex personality and powerful abilities. Fans might be interested in seeing her in a more central role without Issei around.