Well, in this fanfiction, Issei is the obvious main character. Regarding Kuoh Academy, Rias is a very likely main character. She is Issei's master in the Occult Research Club and has a deep connection with him. Akeno, being Rias' second - in - command and also having a special relationship with Issei, is also a key character. Koneko, with her own relationship with Issei, would also be prominent. And don't forget about Sona Sitri from the student council. She might be interested in Issei's life as well due to the power dynamics and relationships within the academy.
Issei is the focal point as his life is the subject. But from the academy, apart from the ones mentioned above, there could also be other club members from the Occult Research Club. Also, teachers or the student council members who might have a vested interest in Issei's activities. They could all play important roles in observing, reacting to, and potentially influencing Issei's life as depicted in the fanfiction.
I'm not sure specifically as it depends on the particular fanfiction. It could be about the characters from Kuoh Academy observing Issei's life in a way that might include his daily adventures, his relationships, or his growth as a character within the fan - created narrative.
Obviously, Naruto would be one of the main characters. He brings his ninja skills, his determination, and his go - get - it attitude. Rias Gremory could also be a main character. She is a powerful devil in Kuoh Academy and her leadership skills and her relationship with Naruto could be a central part of the story. Issei Hyoudou could also play a major role as he is a key figure in the Kuoh Academy setting and his interactions with Naruto would be interesting.
Rias could be a character who betrays Issei in some fanfictions. If she were to face a difficult decision between protecting her family's reputation and standing by Issei, she might choose the former. Another possibility is Akeno. If she were to be influenced by some ancient evil power that made her turn on her friends, Issei could be a target.
Obviously, characters from Konoha will be central. Naruto might be one of the main characters as he often represents the heart of Konoha. His ability to change things could be key in how Konoha responds to the future it sees.
Since it's strq related, the main characters are probably the members of strq.
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.
Obviously, Team Minato itself is the main focus. This includes Minato Namikaze, who is the leader of the team. He is a very powerful ninja with his Flying Thunder God Technique. Then there's Kakashi Hatake, a young and talented ninja who is known for his Sharingan. Obito Uchiha is also a key character, with his Uchiha blood and his dreams of becoming Hokage. And finally, Rin Nohara, who plays an important role in the team's dynamics.
Obviously, the main characters from the 'Fairy Tail' anime such as Natsu, Lucy, Gray, and Erza are likely to be the main characters in this fanfiction as well. Since it's about them watching the anime, they would be at the center of the story.
Well, without actually reading it, it's hard to say precisely. But generally, it might be a fanfiction where a character named DxD watches Issei's life unfold. It could involve DxD observing Issei's adventures, relationships, and growth in the story's fictional world.
He'd be a bit of an oddity. His British wizarding ways would contrast with the Japanese - inspired setting of Kuoh Academy. But his kind heart would help him find a place. He might join some clubs related to magic or mystery, if there are any.