A great concept for a 'jojo persona crossover fanfiction' would be a tournament - style story. Characters from both universes are forced to participate in a battle royale. The Jojo characters would bring their Stands, and the Persona characters would have their Personas. The battles could be intense, with different strategies emerging. For instance, a Persona user might try to use psychological attacks against a Jojo character who is more used to physical combat with their Stand. And the story could also explore how the two groups of characters interact and form alliances outside of the battles.
One idea could be to have the Stand users from JoJo interact with the Personas in a battle royale - style scenario. Maybe the JoJo characters are transported to the Persona universe and have to figure out how to use their Stands alongside the Personas to defeat a common enemy.
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.
How about a story where the Avengers are pitted against Dio? The Avengers would have to deal with Dio's time - stopping ability with their own powers. Iron Man could try to create a device to counteract Dio's time stop, while Captain America uses his strategic skills to lead the fight against Dio's minions.
One idea could be a crossover between 'Jojo' and 'Harry Potter'. Imagine Jotaro in Hogwarts, using Star Platinum to perform magic in a unique way. Another could be a 'Jojo' and 'My Hero Academia' crossover, where the stands of 'Jojo' characters interact with the quirks of 'My Hero Academia' characters. Or perhaps a 'Jojo' and 'Lord of the Rings' crossover, with Jojo characters on a quest in Middle - earth.
One idea could be to have the Jojo characters enter a popular video game world like Minecraft. They could use their stands to build amazing structures or fight off mobs in unique ways. For example, Star Platinum could be used to mine blocks at super - fast speed.
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.
Maybe there's a situation where the Velvet Room attendants from Persona 3, 4, and 5 realize that there's a threat to the collective unconscious that only the combined efforts of the three protagonists can stop. So, they somehow manage to bring the characters together. The characters then start to learn from each other's combat styles and ways of forming bonds with their friends, which helps them in their fight. For example, the protagonist of Persona 3 could teach the others about his experiences with death and how to face it head - on in battle, while the Persona 4 protagonist could share his knowledge of reading people and finding the truth behind the mysteries. The Persona 5 protagonist could contribute with his skills in stealth and infiltration.
A great plot for Persona 4 crossover fanfiction could be a crossover with the 'Sword Art Online' universe. The Persona 4 gang could be trapped in the virtual world of SAO and have to use their Personas to defeat the bosses and escape. Or, they could cross over with the 'My Hero Academia' world. Here, they could attend the hero school and learn new ways to use their powers, while also sharing their Persona knowledge with the MHA characters. Also, a crossover with 'Harry Potter' would be interesting. They could attend Hogwarts and discover that their Personas have unique interactions with magic.
A crossover with a post - apocalyptic world setting. The Persona 3 characters find themselves in a world destroyed by some great cataclysm. They have to use their Personas not only to fight the Shadows that lurk in this new world but also to survive against other desperate survivors and new, mutated threats. They might also have to find a way to restore the world using their Persona powers.
A cool plot could involve a powerful Persona user from Persona 3 who has somehow lost their memory and ends up in Inaba (the setting of Persona 4). The Investigation Team from Persona 4 takes them in and tries to help them regain their memory. As they do, they discover that this person holds the key to preventing a major catastrophe that will affect both their worlds.