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.
When developing the characters in this fanfic, consider their physical appearances as well. The OC's appearance can say a lot about them. For example, if they have a unique hair color or style, it could be related to their heritage or a sign of their rebellious nature. For Fem Vali, her appearance might change slightly as she becomes closer to the OC. Maybe she starts to wear a certain accessory that the OC gave her. In terms of their personalities, you can make the OC a bit of an outcast at first, which makes Fem Vali's interest in them more interesting. And for Fem Vali, you can show her as initially cold but warming up to the OC over time through small, meaningful interactions.
One popular theme is the exploration of Vali's character growth in a female form. In many fanfictions, she might face challenges related to her new gender identity within the context of the Highschool DxD universe. Another theme could be her relationships, like forming new friendships or rivalries with other characters.
Well, in some fanfictions, the female Vali can be more in touch with her emotions. The original Vali is often portrayed as a bit more stoic and focused on power. As a female, she might show more vulnerability, while still maintaining her strong and competitive side.
One popular type of fanfiction about Vali Lucifer in Highschool DxD could be his power development. Writers might explore how he further hones his abilities, perhaps by training in new, secret locations. This could involve him facing off against powerful, previously unknown foes that push his limits and force him to unlock new levels of his power.
Character relationships are a big part. Vali's interactions with other characters from Highschool DxD, like Issei, are given more depth. There could be rivalries explored in more detail or even unexpected alliances formed. Fanfictions might also delve into Vali's past more, like his upbringing in the devil society, which gives readers a better understanding of his motives and actions in the story.
A plot idea could be Vali being sent on a secret mission by the Devils. He has to infiltrate an enemy stronghold that is rumored to be developing a weapon that could destroy the balance between the three factions. Along the way, he teams up with some unexpected allies, including some from the Angel faction who also don't want the balance to be disrupted.
Perhaps a plot where the members of Vali's harem start developing new and unique powers. They then have to train together to control these powers while also facing threats from other factions in the Highschool DxD universe. This would involve a lot of character development and relationship building within the harem.
Well, you could make an OC that is a half - angel, half - devil. This would give the character a very complex backstory and internal conflict, especially in the world of Highschool DxD where the angels and devils have their own politics and power struggles. Also, for the OP part, this OC could have a special ability to combine angelic and demonic powers in a new and powerful way.
You can try websites like Fanfiction.net. It has a large collection of fan - made stories for various series, including Highschool DxD. Just search for 'Highschool DxD Vali' and you'll get a list of relevant fanfictions.
One popular fanfiction might be those that explore Vali's backstory more in - depth. For example, stories could detail his training and how he became so powerful.