Maybe the OC is a descendant of an ancient race that was once closely associated with the power of Divine Dividing. They come to the high school to find out more about their heritage and end up getting involved in the power struggles between the different factions in the DxD world. This could involve making alliances and enemies along the way.
Another fanfiction concept could be that the OC has a unique form of the Divine Dividing that doesn't just split power but also can split time or space in a limited way. This would make them a very interesting character as they try to figure out how to use this power for good while also keeping it a secret from those who might misuse it.
The OC's abilities related to Divine Dividing could be developed in different ways. They could start with basic power - splitting physical objects. As the story progresses, they learn to split intangible things like magical barriers or even the auras of other powerful beings. This growth in power can be tied to their emotional and mental development throughout the fanfiction.
The popularity also lies in the fact that it allows fans to expand on the existing lore. With Divine Dividing, there are so many possibilities. For example, fanfiction can show how the power could be used in different battles or how it could affect relationships between characters in ways not shown in the original series. This makes it very appealing to fans who want more from the Highschool DxD universe.
Another interesting one is 'In the Shadow of Divine Dividing'. It delves deep into the backstory of the Divine Dividing in the context of Highschool DxD. It weaves in elements of mystery and intrigue as it reveals secrets about the power that were previously unknown.
A plot could involve the mute OC being a new transfer student in the school. Their muteness makes them an object of curiosity and some characters might initially misjudge them.
For character development, the mute OC might struggle with feelings of isolation at first. But as the story progresses, they could form deep bonds with other characters who learn to understand them in unique ways. For example, a character might be able to sense their emotions, leading to a really heartwarming friendship.
One idea could be to create an OC youkai who is a kitsune. The kitsune could have unique powers like illusion - making and fire manipulation. It could start as an enemy to the main characters in Highschool DxD but later become an ally due to shared goals, such as protecting the human world from a greater evil.
One idea could be to create an OC who has a Sharingan that has unique abilities. For example, instead of just the normal powers like predicting movements, it could have the ability to see through illusions created by devils in the Highschool DxD universe. The character could be a transfer student, perhaps from a hidden clan that has a connection to both the Naruto world (where Sharingan is from) and the Highschool DxD world. Their backstory could involve some sort of experiment or curse that led to them having the Sharingan.
One idea could be that the OC with the Vritra Gear has to hide its true power at first. Maybe they are new to the school and don't want to draw too much attention. As the story progresses, they gradually reveal their abilities during battles against other supernatural beings.
You could write about an OC who is a half - angel, half - devil. Their internal struggle between the two natures and how they fit into the world of Highschool Dxd, trying to find their place among the devils, angels and fallen angels. It could explore themes of identity and acceptance.
An interesting OC for a Highschool DxD fanfiction could be a half - angel, half - devil. Their internal struggle between the two natures would make for a great character arc. They could be trying to find their place in the world where angels and devils have their own agendas, and they don't fully belong to either side.