What are some interesting plot ideas for an 'illya x highschool dxd fanfiction'?

Perhaps there could be a crossover of the two schools. The students from Beacon Academy and Kuoh Academy could have an exchange program. Yang might get into some friendly (or not so friendly) competitions with the devils in terms of strength, while Weiss could be fascinated by the more formal and complex social structure in the Highschool DxD world.

One idea could be a character from Prototype having to adapt to the supernatural world of Highschool DxD. For example, Alex Mercer could end up at Kuoh Academy and have to deal with the devils and angels while also trying to figure out his own powers in this new context.

One idea could be an OC who is a transfer student with a unique power that no one in the Highschool DxD universe has seen before. This power could attract the attention of the main characters and lead to various adventures and alliances.

The interaction between Illya and Rias would be really interesting. Rias is a powerful devil with a lot of charm and leadership. Illya, on the other hand, is a magical girl with her own set of powers. They could start off as rivals, both vying for the attention or respect of other characters, but then realize they have more in common and can work together.

One idea could be that Naruto somehow gets transported to the High School DxD world and has to use his ninja skills in the battles there. Maybe he teams up with Issei and they combine their powers in a unique way.

One plot idea could be Naruto being transferred to the Highschool DxD world and having to adjust to the new school environment while also dealing with the supernatural elements. He could form an unexpected friendship with Ophis, perhaps over their shared experiences of being different from the norm in their respective worlds.

One idea could be that Harry Potter somehow gets transported to the world of Highschool DxD. He could use his magic skills in the unique battles and challenges there. For example, he might use spells like Expelliarmus to disarm the devils or fallen angels during a fight.

Maybe the OC is an artist who can create magical art. Akeno is fascinated by this art and the emotions it evokes. They could start collaborating on projects that are not only artistic but also have a deeper meaning in the context of the Highschool DxD universe. For instance, creating art that can temporarily shield them from attacks or art that can influence the minds of their enemies. Their relationship could grow as they explore the potential of the OC's art together.

Maybe the OC Sitri is from a different branch of the Sitri family that has been in hiding. Their appearance in the story could stir up old rivalries or create new alliances. They could bring with them ancient knowledge or artifacts that change the power dynamics in the Highschool DxD world.

Another plot could involve the Quincy from Bleach. Uryu could be mistaken for a Devil by some of the Highschool DxD characters because of his unique powers. This misunderstanding could lead to a conflict at first, but then they realize they are all on the same side against a greater threat, like a powerful fallen angel who is trying to start a war between the Hollows, Devils and Quincies.