You could create an OC for your Persona OC fanfiction who is an artist. This artist OC could use their art as a way to understand and even manipulate the Metaverse. For example, they might draw scenes from the Metaverse that give clues about upcoming events or hidden locations. Their art could also be a form of therapy for other characters who are struggling with their dual lives in the real world and the Metaverse.
One idea could be creating an OC who is a transfer student with a unique past related to the Dark Hour. For example, they might have had a family member affected by Shadows long before coming to the school. Another idea is an OC with a special ability that doesn't quite fit the normal Persona - using skills that are more about mental manipulation rather than direct combat. And you could also have an OC who is initially a skeptic about the whole Persona thing but slowly gets drawn into it.
Well, you could have an OC that is a skilled hacker who gets involved with the Phantom Thieves by accident. They might have a Persona that represents a famous code - breaker from history. Also, an OC who is a foreign exchange student from a country with a very different cultural background could bring in new elements to the fanfiction. Their Persona could be influenced by their home country's folklore. Maybe an OC who is a prodigy artist and uses their art skills to create powerful items in the Metaverse, with a Persona related to a great artist from the past.
A male oc who is an undercover detective sent to Inaba to investigate the strange disappearances could also be a great idea. He would have to balance his real identity and mission with fitting in with the group of Persona users. His detective skills could come in handy during dungeon exploration and solving the mysteries behind the Midnight Channel.
Well, an interesting plot could involve an OC that is a transfer student, just like the protagonist. But this OC has a hidden past related to the Metaverse. Maybe they were experimented on by a shadowy organization in their home country, and this gives them a different perspective on the Metaverse compared to the Phantom Thieves. Their goal could be to find out who was behind those experiments and get revenge. Along the way, they form a bond with the group and learn new ways of using their powers.
One idea could be the characters from Persona 4 and Persona 5 swapping their worlds. So the Phantom Thieves end up in Inaba and have to deal with the Midnight Channel mystery. And the Investigation Team finds themselves in Tokyo and gets involved in the Metaverse. It would be really cool to see how they interact with the different environments and characters.
In some persona 4 oc fanfiction, an OC might be a detective who is secretly investigating the strange happenings in Inaba. This OC could have their own set of skills and resources, and as they dig deeper, they discover connections between the real world and the TV world that the main characters haven't noticed yet. Their investigations could also put them in danger and lead to some intense action scenes.
How about 'Persona 4 OC's Adventure with Naoto: A Fanfiction Tale'? This title not only indicates the main characters which are the OC from Persona 4 and Naoto but also implies that there will be an adventure involved. It gives a sense of excitement and mystery which might attract readers to check out the fanfiction.
One idea could be a story about their training days before they became the wardens in Velvet Room. Maybe they had to face some tough challenges together and how they overcame those as sisters. Another could be a fanfiction where they interact with the Phantom Thieves in a more casual way outside of the Velvet Room, like going on a simple adventure in the real world.
Well, you could write a fanfiction where the Messiah in the DxD world has to adapt to the modern and often chaotic world of DxD. For instance, dealing with the different races' cultures and politics. The Messiah could start as an outsider and gradually become an important figure in uniting different groups against a powerful evil force that wants to disrupt the balance in the DxD world. This would involve a lot of character development and exploration of the DxD world's rules and hierarchies.
A really interesting plot could involve a new threat that emerges and can only be defeated by combining the powers and skills of the Persona 3 and 5 characters. For example, the combat styles of the two groups are different. The SEES members are more used to fighting in the Dark Hour, while the Phantom Thieves operate in the cognitive world. They would need to learn from each other's strategies. And on a character level, the more serious and reserved characters from Persona 3 could interact with the more flamboyant and confident characters from Persona 5, leading to some really interesting dialogue and relationship building.