One common theme is the clash of different ideologies. Since Alexander Anderson has his own set of beliefs and values, when he enters the High School DxD world, which has its own complex moral and power structures, there is often a conflict. For example, his strict sense of justice might not always align with the more chaotic and self - interested nature of some DxD characters.
There's also 'Anderson at High School DxD: A New Beginning'. In this fanfiction, Anderson enters the high school DxD universe and has to adapt to its rules. It's interesting to see how his character, which has different values from the original DxD characters, interacts with them. He brings a new sense of order and discipline to the chaotic high school DxD environment.
In a Naruto and High School DxD fanfiction, there could be a scenario where the protagonists of both stories meet in a neutral dimension. Issei from High School DxD might be intrigued by Naruto's ninja skills and determination. Naruto, in turn, could be curious about Issei's Sacred Gear. They could start training together, sharing their knowledge and skills, and ultimately have to face a common enemy that threatens both their worlds.
One idea could be a crossover where Naruto's world is invaded by some dark forces similar to those Anderson has faced. Naruto, with his ninja skills, teams up with Anderson, who uses his holy powers. They start to learn from each other's fighting styles and develop a mutual respect. Naruto could teach Anderson about chakra and how to use it in combat, while Anderson could show Naruto the power of faith - based combat and the use of holy relics.
Faith is also a big theme. Anderson's strong religious faith drives his actions against vampires. His unwavering belief in God and the Church's teachings colors his every encounter with the undead. And of course, there's the theme of power. Who has more power, the holy power of Anderson or the dark powers of the vampires? It's often a central question in these fanfictions.
Maybe Naruto, as Anderson, is part of an organization that fights against supernatural threats. He uses his Uzumaki bloodline abilities in a new and unique way. For instance, his ability to heal quickly could be seen as a form of Anderson's regenerative powers. And he would be constantly at odds with those who oppose his extreme methods of dealing with enemies, just like Anderson in his own story.
One idea could be a crossover where Alexander Anderson, with his combat skills and religious fervor from his own universe, is transported to the Harry Potter world. He might initially be seen as a threat due to his extreme methods, but then he teams up with the Order of the Phoenix to fight against dark wizards who are dabbling in some form of dark magic that has religious connotations in his view.
One possible fanfiction could be about Naruto characters attending the school in High School DxD. For example, Naruto's positive and determined attitude might clash with the more complex social and power dynamics in the DxD world. He could make new friends or even rivals among the devils, angels, and fallen angels.
One idea could be that Ben Tennyson somehow gets transferred to the world of High School DxD. He has to keep his alien forms a secret while dealing with the devils, angels, and fallen angels in the school. Maybe his Omnitrix could be misinterpreted as some kind of powerful devil device.
One possible fanfiction could be about Naruto characters somehow ending up in the world of High School DxD. Maybe Naruto's skills in combat and his determination would make him a formidable opponent in the battles that often occur in the High School DxD universe. He could form interesting alliances or rivalries with the characters there.