Power growth is a very common theme. Writers often explore how the characters can become stronger in different ways compared to the original story. Another common theme is relationship development, like the romantic relationships between characters.
Well, there's a fanfiction called 'Issei's Ascent'. In this one, Issei goes through some unique character development that's quite different from the original plot. There are also fanfictions that focus on the side characters more, like 'The Knights of Gremory', which gives more depth to the Gremory group.
One common theme is self - discovery. The human OCs often find themselves in a new and strange world of devils and other creatures, and they have to figure out who they are in this context. For example, they might discover hidden powers or a new purpose in life.
One idea could be exploring a new character's journey in the Highschool DxD human world. Maybe a transfer student who has a unique power or ability that shakes up the status quo among the devils, angels, and fallen angels. They could start off as an unknown and gradually form alliances and rivalries.
One idea could be to have Naruto end up in the DxD world through a strange portal. He might bring his unique ninja skills and chakra system, which would be a huge shock to the devils and other beings in the DxD world. Maybe he teams up with Issei to fight against a common enemy that threatens both the ninja world and the DxD world.
First, familiarize yourself with the original Highschool DxD series. Know the characters, the rules of the world, like the power hierarchies among devils, angels, and fallen angels, and the general plotlines. Then, think about the character you want to focus on. If it's a human, decide their backstory, their goals, and how they will interact with the supernatural elements.
Naruto and Rias could be a great pairing. Naruto's positive and determined nature would complement Rias' leadership and strong - willed personality. They could work together to protect their respective groups and also learn from each other's powers and cultures.
Sure. 'A New Devil in Highschool DxD' is a great one. It has an interesting human OC who brings a fresh perspective to the story. The plot is engaging as the OC tries to navigate the complex world of devils and other supernatural beings in the Highschool DxD universe.
Well, Tiamat in her human form in fanfiction could be depicted as having a slender yet strong physique. Her skin might be pale as porcelain, giving her an almost ethereal look. She could be dressed in elegant, flowing robes that seem to move with a life of their own, and she may possess some sort of magical or supernatural jewelry that enhances her already considerable power. Maybe she has a soft, melodious voice that can charm or intimidate depending on her mood.
The human OC can be developed by giving them unique abilities. For instance, they could have a special power that Rias doesn't have or understand. This would make them stand out and be a threat to Rias. Another way is through their backstory. A tragic or interesting backstory can make the readers sympathize with the OC and understand their motives for bashing Rias.