The story mainly follows Issei Hyodo, a high school student who gets killed on his first date and is later resurrected as a devil. He then becomes part of the Occult Research Club at his school. There, he gets involved in various battles against other supernatural beings, all while trying to become stronger and also dealing with his new devilish desires and relationships with his female comrades.
Well, there are prequel novels that offer background on some of the characters and events. Also, there are companion novels that explore additional adventures and story arcs within the same world.
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.
The 'Nishan High School story' could potentially cover a wide range of topics. It might involve the school's participation in sports competitions, where the students showed great teamwork and determination. Or perhaps it's about a cultural event held at the school that brought the whole community together. There could also be a story of a student's journey of self - discovery within the walls of Nishan High School.
In a High School DxD fanfiction with the Skyrim Dragonborn, he would likely face a culture shock. In Skyrim, he is used to a medieval - like setting with different races and magic systems. In High School DxD, it's a modern - day world with a complex society of devils, angels, and humans. However, his adaptability, which he has shown in Skyrim by traveling to different regions and dealing with various quests, would help him. He could potentially introduce new forms of magic or combat techniques from Skyrim, which would disrupt the existing power balance in High School DxD.