One idea could be a female OC who is a transfer student with a unique Sacred Gear that no one has seen before. This could lead to all kinds of adventures as the characters in the Highschool DxD world try to figure out what it is and how powerful it could be.
You can make your female OC memorable by focusing on her goals. Let's say she's determined to bring peace between the three factions (devils, angels, and fallen angels). This gives her a big - picture goal that can drive the story forward. Her flaws are also crucial. If she's overly confident and it sometimes gets her into trouble, like getting into battles she's not fully prepared for, it makes her more relatable and human - like in a world of powerful beings.
An OC (Original Character) in a Highschool DxD fanfiction having the Rinnegan could be an extremely powerful and unique addition. The Rinnegan, from the Naruto universe, brings a whole set of abilities like the Six Paths powers. In the context of Highschool DxD, this OC could use these powers in various ways. For example, the ability to see chakra could be translated into seeing the magical energy in the DxD world. They could use the gravitational powers of the Rinnegan to manipulate the environment during battles against devils, angels, or fallen angels. It would make for a very interesting and overpowered character in the Highschool DxD fanfiction setting.
The OC, as the Son of Sparda, could fit in by being a new and powerful entity. He might be initially seen as an outsider, but his powers would quickly draw attention. He could become involved in the power struggles between the different factions in Highschool DxD. For example, the devils might try to recruit him, while the angels might be wary of his presence. His unique abilities would also make him a valuable ally or a fearsome opponent. And in the high school setting, he could be a bit of an enigma to the other students, both human and supernatural.
First, you need to define their personality clearly. Are they slutty because of a past trauma or is it just their natural inclination? This backstory will help shape their character. For example, if it's due to a past betrayal, it can add depth to their promiscuous behavior.
A unique and well - developed OC. If the original character has an interesting backstory, personality, and goals within the world of Highschool DxD, it can make the fanfic engaging. For example, if the Gamer OC has a special power or ability that is different from the existing characters in the series.
One idea could be a story where the OC is a new student at the school and catches Fem Vali's attention during a battle training session. Their relationship could start as a rivalry but gradually turn into a deep friendship and then something more romantic as they discover they have more in common than they thought.
The main reason is the freedom it gives to fans. With an SI OC, readers can see their own ideas and personalities injected into the Highschool DxD world. It's like they get to be part of the story in a more direct way.
Well - developed characters make it interesting. If the original character (OC) has a unique personality, backstory, and goals, and their relationship with Gabriel is complex and evolving, it can be really engaging. For example, if the OC is a half - demon who struggles with their identity and Gabriel helps them come to terms with it.
When writing a believable male OC for a Highschool DxD fanfic, consider his flaws. No one is perfect. Maybe he's a bit clumsy or has a short temper. These flaws make him more human. His relationships also play a big role. How he interacts with the other characters in the Highschool DxD universe should be based on his personality. For instance, if he's an introvert, he might be hesitant to join social events. And his goals and dreams should be clear. Whether it's getting better grades, impressing a girl, or becoming a stronger fighter, it gives direction to his character.