Well, a common theme is alternate universes. Writers like to create their own versions of the Highschool DxD world, where different events occur. It could be a world where the main character makes different choices early on in the story. Also, the theme of character backstories is quite popular. Fanfiction authors expand on the backgrounds of the characters, giving more depth to their personalities and motives. And some fanfictions are centered around battles and tournaments, with more intense and creative fight scenes than in the original novels.
One common theme could be the development of a romantic relationship between male characters within the 'Highschool DxD' universe. For example, a relationship between two of the devil characters that involves them overcoming challenges together, like dealing with rivalries from other clans while also exploring their new - found feelings for each other.
One popular theme could be the relationships between the characters. For example, exploring the romantic and sometimes more intense relationships between the main character and the various female characters in the series. Another theme might be the power dynamics within those relationships, as there are different levels of power among the characters in Highschool DxD.
One popular theme is the exploration of relationships between female characters. In Yuri Highschool DxD fanfiction, writers often focus on the emotional bonds and interactions between the female characters. Another theme could be the development of unique powers or abilities within the Yuri context of the story. For example, a character might discover a new power that is related to her relationships or her own self - discovery. Also, the theme of friendship and loyalty among the female characters is quite common. They support each other through various challenges in the high school setting, which is full of supernatural elements in the Highschool DxD universe.
Power development is also a common theme. Gasper has his own set of powers, and fanfiction may delve into how he hones them. Maybe he discovers new ways to use his vampire abilities, or he trains with other characters to become stronger and more in control of his powers.
One popular theme is power - ups. In both Highschool DxD and Campione, power is a significant aspect. Fanfictions often explore characters getting new and stronger powers, and how they use them. For example, in Highschool DxD, a fanfic might focus on Issei getting a new form of his Boosted Gear.
One popular theme is the relationship development between the female characters. It could be about how they gradually fall in love, overcome obstacles in their relationship, like dealing with the opinions of other characters in the Highschool DxD world.
One common theme could be the exploration of unique power dynamics. Since Highschool DxD has a complex system of powers, in futanari fanfiction, it might show how these characters with different genders and powers interact. For example, a futanari character might have a special power that affects the relationships and battles within the story.
For Naruto fanfiction, redemption arcs for villains can be a popular theme. Writers might explore how characters like Sasuke could have a different path to redemption. Another theme is time - travel, where characters go back in time to change events. In Highschool DxD fanfiction, exploring the backstories of the devil characters more deeply is a theme. Also, crossovers between Highschool DxD and other anime are becoming more popular, like a crossover with Bleach or One Piece.
One popular theme is adventure. Yasaka could be on a journey to protect her territory or find a powerful relic. Another theme is friendship. She might form new alliances with other characters from the Highschool DxD universe. And of course, there's the theme of power - how she gains or uses her power in different situations.
Another popular theme is alternate relationships. The multiverse allows for different pairings between characters that might not be possible in the original story. It gives a fresh perspective on the characters' personalities and how they interact with others.