The fanfiction could revolve around a new character who has the ability to traverse between the Splatoon and Persona 5 worlds. This character discovers a conspiracy that if not stopped, will merge the two worlds in a disastrous way. The character enlists the help of both the Inklings and the Phantom Thieves. They have to overcome their differences in fighting styles and cultures to save both their worlds. The inklings' turf war strategies could be adapted to the battles in the Metaverse, and the Phantom Thieves' stealth could be useful in the Splatoon world.
Makoto Niijima from Persona 5 and an Inkling girl could be main characters. Makoto is intelligent and strong - willed. The Inkling girl could bring her unique ink - related abilities. They could work together to figure out the strange phenomena that are occurring between the two worlds. Makoto could use her detective skills, while the Inkling girl could use her agility and ink - based defenses.
Maybe the Velvet Room attendants from both games somehow get their worlds mixed up. Igor from Persona 5 and Margaret from Persona 4 have to work together to set things right. This leads to the characters from both games interacting. The Phantom Thieves might learn some new combat techniques from the Investigation Team and vice versa. They could then use these new skills to face a common threat that emerges from the merging of their two realities.
One interesting plot could be that Bowser teams up with the Octarians in the Splatoon world. He wants to use their ink technology to take over both the Mushroom Kingdom and the Splatoon world. Mario has to then form an alliance with the inklings. He travels through different ink - filled levels, learning new skills like swimming in ink and using ink - based weapons. Along the way, he discovers secrets about the connection between the two worlds. They finally face Bowser and the Octarian leader in a huge battle where Mario combines his classic moves with the ink - powered attacks of the inklings to save both worlds.
Well, perhaps the story could start with a strange distortion in the Metaverse that links the two universes. Some of the characters from Persona 4 start having dreams about the events in Persona 5's Tokyo, and vice versa. This leads to a meeting between the two groups. They then discover that an ancient evil, long forgotten in both their histories, is trying to use the connection between the two worlds to gain enough power to rule over everything. The characters would have to learn about each other's powers and personalities quickly in order to stand a chance against this new foe.
A great plot could be that a new threat emerges that has the power to erase the memories of people in both Persona 4 and Persona 5's worlds. The characters from both games must work together to find the source of this threat. The Phantom Thieves could use their infiltration skills, while the Investigation Team could use their detective - like skills to gather clues. As they progress, they discover that the root of the problem lies in an ancient evil that was once sealed away but has now been awakened due to some modern - day events.
Perhaps the fanfiction focuses on the cultural clash between the two groups. The Persona 4 characters are from a small town, while the Persona 5 crew is from the big city. Their different ways of handling things and their unique Personas could lead to some interesting interactions. For example, Yu and Joker might have different leadership styles that they have to reconcile in order to succeed against the shadows.
One possible plot could be a story where the Finkling and the male human meet in an unexpected place, like a shared love for art in a human - Inkling cultural exchange event. They start to learn about each other's worlds. The Finkling shows the male human the unique features of Inkopolis, like the Turf War battles, while the male human introduces the Finkling to human hobbies such as playing musical instruments. Their friendship gradually develops into a deeper bond as they overcome differences and challenges together.
In this fanfiction, the OC could be a loner who is misunderstood by most people in Inaba. Naoto, on the other hand, is respected but also somewhat isolated because of their unique position. They meet by chance during a strange event related to the Persona world. At first, they are wary of each other. But as they start to work together to solve the mystery behind the event, they realize they have more in common than they thought. The OC helps Naoto to open up more on an emotional level, and Naoto teaches the OC how to better use their Persona powers. Their relationship gradually evolves from a reluctant partnership to a strong bond that is crucial for saving Inaba from a greater threat that is looming over the town.
In this fanfiction, the OC could be a detective - in - training who comes to Inaba to solve some cold cases. Yukiko gets involved when some of these cases seem to be related to the TV World. They team up, with Yukiko providing her knowledge of the town and the OC using their detective skills. As they work together, they develop feelings for each other. But they also have to deal with the danger of the Shadows and a mystery figure who seems to be controlling them, all while trying to figure out their relationship.
One possible plot could be that the characters from RWBY end up in the Persona universe and have to learn how to use Personas to fight the Shadows. For example, Ruby could discover her Persona is related to her speed and scythe skills, and she uses it to quickly dispatch enemies. The team would also have to deal with the social aspects of the Persona world, like building relationships to strengthen their Personas.