Another concept is the exploration of different relationships. In highschool dxd system fanfiction, characters might form new alliances or romances that weren't as prominent in the official story. This can lead to some really engaging character development.
Another concept could be the exploration of different power systems. Hellsing has its own set of rules regarding vampire powers, holy weapons, etc., while Highschool DxD has the Rating Game system and the various devil powers. Fanfiction might play around with how these power systems interact, like if a character from Hellsing were to participate in a Rating Game or how a devil from Highschool DxD would fare against a Hellsing vampire.
One interesting concept could be the exploration of different character relationships in a more subdued or 'silent' way. For example, how the main character might form unexpected friendships without the typical high - energy drama. Another could be the re - imagining of the story's settings in a more peaceful or reflective manner.
In Aizen Highschool DxD fanfiction, a cool concept might be how Aizen's Zanpakuto abilities would translate in the Highschool DxD setting. His Shikai and Bankai could have new and unexpected effects. Maybe his illusions could be used to deceive not just in battle, but also in the social and political intrigue that is so common in the Highschool DxD world among the different factions.
One interesting concept could be a crossover where the characters from Highschool DxD encounter Slenderman. Maybe the devils in Highschool DxD are intrigued by Slenderman's otherworldly and spooky nature. They might try to either recruit him or fight him, depending on their motives.
One interesting concept could be the crossover of the Highschool DxD world with the eerie and mysterious Slender Man. For example, how the characters in Highschool DxD, with their unique powers and personalities, would react to the presence of the Slender Man. Maybe the devils in Highschool DxD would try to make a deal with the Slender Man or fight against him to protect their territory.
In Gilgamesh Highschool DxD fanfiction, there might be concepts like Gilgamesh forming alliances or rivalries with the devils, angels, and fallen angels in the Highschool DxD world. His vast treasures from his own story could also play a role, perhaps being used as bargaining chips or powerful weapons in the battles that often occur in the Highschool DxD setting.
One interesting concept could be alternate universes where the characters have different powers or relationships. For example, a fanfic might explore a world where Issei has angelic powers instead of his usual devil powers. Another concept could be character crossovers, like bringing in characters from other anime into the Highschool DxD universe.
One interesting concept could be the change in character dynamics. For example, a male character turned female might face different challenges in the school's social hierarchy. They might have to deal with new forms of attention or expectations.
Well, often in Highschool DxD OC Demon Fanfiction, the origin stories of the OC demons are really engaging. Some might be descendants of ancient and powerful demon clans that were thought to be extinct. Their struggle to prove themselves in a world full of strong demons can be a great concept. Also, the way they adapt to the modern world of Highschool DxD, which is a mix of the supernatural and the normal high school life, is interesting. They might have to deal with things like using modern technology while still having their old - fashioned demon values.
One interesting concept could be the combination of Naruto's ninja abilities with the supernatural elements from Highschool DxD. For example, Naruto's shadow clone jutsu might be used in a creative way in the Highschool DxD setting, like having clones help out in battles against devils or angels. Another concept could be the character interactions. If characters from Naruto like Naruto himself or Sasuke were to interact with the characters from Highschool DxD such as Issei, there would be a lot of cultural and power - based clashes and exchanges. It could also be interesting to see how the different power systems mesh together, like chakra and the sacred gears in Highschool DxD.