One common theme is the exploration of their relationship. Since they come from different backgrounds in the anime universe, fanfictions often delve into how they get to know each other better and form a connection.
One common theme is the relationship development between Issei and Kuroka. It often explores how their unique personalities interact and grow closer. Another theme could be power dynamics, as both characters have their own powers in the original story.
You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own (AO3). These platforms usually have a wide range of fanfictions, including those related to Issei and Kuroka.
Some popular themes in Issei and Kuroka fanfiction could be adventure. They might go on quests together in the supernatural world of Highschool DxD. Another theme could be relationship development, like how they gradually fall in love and overcome the differences between a human - turned - devil like Issei and a nekomata like Kuroka.
One common theme could be the clash or harmony of different powers. Since Issei might have his own set of powers and Amaterasu is a significant figure in mythology with her own powers, their interaction in terms of power dynamics can be a theme. For example, how they combine their powers to face a common enemy.
Friendship is a common theme. They might show how Issei and Gasper support each other through different challenges in their fictional world.
Love and friendship are often explored as well. It could start as a friendship that gradually develops into something more. Or perhaps they are forced to work together due to some external threat and in the process, they develop deep feelings for each other. The stories might also touch on themes of loyalty and sacrifice as their relationship progresses.
One common theme is the development of their relationship. Since they often start with a certain dynamic in the original source, fanfictions like to explore how that relationship deepens and changes over time.
Another theme could be adventure. They might go on quests together, facing various challenges that test their relationship and individual strengths. For example, they could be on a mission to save a kingdom or defeat a powerful enemy.
Friendship is also a big theme. They could start off as strangers and gradually become good friends, helping each other out in tough situations. It's about building a bond based on mutual respect and shared goals. And sometimes, there's the theme of redemption. If Kuroka has a troubled past, Naruto could be the one to help her find a new path.
The popularity might be due to the interesting characters of Issei and Kuroka. Their unique personalities and the chemistry between them in the original story can be explored further in fanfiction. Also, the 'lemon' aspect often adds a bit of spice and a different take on their relationship that some readers find appealing.