To write a good Naruto x Highschool DxD fanfic, you need to focus on the character interactions. How would Naruto react to the flirty nature of some Highschool DxD characters? How would the devils view Naruto's strong sense of justice? Also, build a believable world. Since it's a crossover, you have to make it seem like these two very different worlds can co - exist. You can do this by creating a common threat or goal. And don't forget about the pacing. Keep the story moving at a good speed, not too slow or too fast. Throw in some action scenes, but also have some quiet moments for character development.
Another aspect could be the cultural differences between the two universes. Naruto comes from a more traditional Japanese - inspired world, while Highschool DxD has a more modern, supernatural - focused world. Fanfics might explore how the characters deal with these differences, like Naruto introducing his values of hard work and friendship to the more power - hungry characters in Highschool DxD.
Naruto would probably be very friendly and curious. He'd be excited to meet all the different types of beings in the Highschool DxD world. He might start by trying to make friends with Issei, sharing his stories about his own battles and adventures in his world.
One idea could be a crossover where Naruto characters end up in the world of Highschool DxD. For example, Naruto himself could be transferred to the school in Highschool DxD. He might use his ninja skills in the battles against the devils and fallen angels there. His shadow clone jutsu could really surprise the characters in the Highschool DxD world.
One popular concept is the power exchange. For example, Naruto's unique jutsu skills being introduced to the Highschool DxD world. Maybe a character from Highschool DxD learning the Rasengan. Another concept could be the character relationships. How would Naruto interact with Issei and his friends? They might form an unlikely alliance against common enemies. Also, the idea of combining the different mythologies in both series is fascinating. The shinobi world's gods and the devils and angels from Highschool DxD could create some really interesting storylines.
When exploring fanfics, keep in mind the quality of writing. Look for ones with good grammar and engaging storylines. Some fanfics might focus on a particular aspect of their relationship, like how they support each other during difficult times in the Highschool DxD world, while others could be more light - hearted and focus on their daily interactions.
There's a fanfic called 'Rias and Issei: A New Adventure'. In this one, they go on a journey together that tests their relationship. The author does a wonderful job of portraying their feelings for each other and the challenges they face as a couple in the world of Highschool DxD.
I really like the fanfic 'Koneko's Heart for Issei'. In this one, it delves deep into Koneko's emotions towards Issei. It starts with her being a bit reserved but as the story progresses, her true feelings start to surface. Another interesting fanfic is 'Issei and Koneko: United'. This fanfic shows how they work together to face challenges in the Highschool DxD world, and their relationship blossoms as they rely on each other.
One great fanfic could be 'Issei and Gasper's Unlikely Bond'. It delves into how their friendship develops in a unique way, with some exciting adventures in the Highschool DxD universe. They face challenges together and support each other, which is really heart - warming.
One of the most interesting plot twists could be the sharing of powers. For example, Naruto's ability to use chakra might combine with the unique demonic powers in Highschool DxD in unexpected ways. Maybe a character from Naruto's world gains a devil fruit - like ability from the Highschool DxD universe. Another could be a character from Highschool DxD learning how to use ninjutsu, which would completely change the power dynamics in their own world.