Who could be the main protagonist in a 'Highschool DxD Zombie' fanfiction?

Issei could still be the main protagonist. His determination and ability to grow stronger could play a big role in any story involving Trihexa. He might be the one to face Trihexa head - on or try to befriend it.

Maybe a rogue ninja from Gaara's world who somehow follows him into the DxD highschool. This ninja could have a vendetta against Gaara and use the chaos of the DxD world to try and take him down. They could also team up with some of the devils who dislike Gaara's presence to create more trouble for him.

It could be a corrupted member of the mafia who has made a deal with a rogue group of fallen angels. This person betrays his own mafia family and works with the fallen angels to create chaos in the Highschool DxD universe. He is very sly and manipulative, always staying one step ahead of the heroes. For instance, he uses his knowledge of the mafia's operations and the power of the fallen angels to set traps for the protagonists.

Issei could be an interesting main character in a 'Highschool DxD Akatsuki' fanfiction. He already has his own journey in the Highschool DxD world, and if he were to interact with the Akatsuki, it would add a whole new dimension to his story. He could learn new techniques from them or even form an alliance against a common enemy.

The devils who oppose Gilgamesh's presence in the Highschool DxD world could be main antagonists. They might see him as a threat to their power and influence in the school.

One possible plot twist could be that some of the devils in Highschool DxD turn out to be immune to the zombie virus due to their demonic nature. This could lead to a power struggle within the group as they decide whether to help the humans or use the situation to their advantage.

Maybe an ancient entity that was sealed away long ago and is now awakened by the presence of the warrior of creation. This entity could be jealous of the new power in the world and see the warrior as a threat to its own plans of domination, thus becoming the main antagonist.

It could be one of the well - known kamen riders like Kamen Rider Decade. Since he has the ability to travel through different worlds, it would be plausible for him to end up in the world of Highschool DxD. He could use his powers to adapt to the new environment and deal with the various challenges there.

Issei would be a popular choice. Since he is the main character in the original series, having him time travel would create many interesting storylines. He could use his knowledge of future events and his growth as a character to change things in the past.

It could be an original character created just for the fanfiction. Maybe a nerdy gamer who has always dreamed of being in a world like Highschool DxD and suddenly finds himself there with incredible powers.