Well, start with a concept. Maybe your oc has a special ability that draws Ann's attention. Then, build their relationship gradually. Don't rush into making them fall in love right away. For the setting, use the locations from Persona 5 such as Shujin Academy. When writing the dialogue, make sure it sounds natural for both characters. Ann has a certain way of speaking, so your oc's dialogue should also match the tone of the story. Also, add some action scenes from the game, like battles with Shadows, to make it more exciting.
The 'joker and his girls persona 5 fanfiction' could potentially focus on various storylines. It might involve adventures that Joker and the girls embark on together. They could be facing off against powerful enemies in the Persona 5 universe. Another possibility is that it explores the emotional bonds between them. How they support each other through difficult times, and how their relationships evolve over the course of the story.
I really like 'The Unlikely Pairing'. It's a fanfiction where the oc is an artist who meets Ann at an art exhibition. Their relationship starts off rocky but slowly blossoms. It has some really interesting dialogue exchanges that show the chemistry between the two characters. It also delves into the world of Persona 5 in a unique way through the eyes of these two characters.
Another possible theme is growth. The girls, with Joker's influence, could be growing as characters. They might be learning new skills, becoming more confident, or maturing in their understanding of the world around them. Also, Joker himself might be growing through his interactions with them.
One popular theme is the female Joker's journey of self - discovery within the Metaverse. Another is her relationships with the other Phantom Thieves, like how she bonds with them and overcomes challenges together. Also, stories might focus on her unique skills and how she uses them in battles against Shadows.
A great storyline might involve a fusion of the two worlds' mechanics. For example, the Velvet Room from Persona could have some connection to Joker's world. The Igor-like figure could offer Joker and his friends some new kind of power or knowledge that they use to combat a common foe. Or perhaps the Persona characters learn about Joker's Metaverse Navigator and try to replicate it in their world, which leads to all sorts of unforeseen consequences and adventures.
Some characters might not get along so well. For instance, a more serious Persona character might find Joker's carefree attitude a bit off - putting. However, as they face challenges together, they would start to understand and respect each other. The Persona characters could introduce Joker and his friends to the concept of the Collective Unconscious in more detail, and the Phantom Thieves could show them how to use their skills in a more urban, modern - day setting. There would be a lot of banter and friendly competition between the two groups as they learn from each other.
In Persona 5 fanfic, a female Joker can bring a fresh perspective. She might have different relationships with the other Phantom Thieves. For example, her interactions with Ryuji could be more nuanced, perhaps with a different kind of banter. Her style of leading the group could also vary, maybe being more empathetic in some ways compared to the male Joker. This can open up new storylines and character developments within the fanfic world.
Makoto is often very level - headed and she can act as a stabilizer in the group. When Akira comes up with a risky plan in the Metaverse, Makoto might be the one to point out the potential flaws and suggest improvements. Ann, on the other hand, is more carefree and might encourage Akira to be a bit more daring. For example, when they are exploring a new Palace, Ann could be the one to say 'Let's just go for it!' while Makoto would say 'Wait, we need to think this through first.'
One possible storyline could be the three of them teaming up for a special heist in the Metaverse. They might use their combined Personas' powers in unique ways to overcome the Shadows. For example, Makoto's strategic mind, Akira's leadership, and Ann's charm could all play important roles in infiltrating a difficult Palace.