A possible plotline is that Percy and a student from Paul's class become friends. The student then helps Percy with a problem in his own world, like finding a lost artifact or solving a mystery that Percy has been struggling with. This friendship could also lead to the two worlds colliding in unexpected ways, with both sides having to deal with the consequences.
One plotline could be that Percy visits Paul's class as a guest speaker and shares his adventures, amazing the students.
Maybe there's a plot where the students in Paul's class get transported to Percy's world and have to learn to survive and adapt. They could be learning about Percy's powers and the rules of his world while trying not to get in too much trouble.
One possible plotline is that Bakugou's boyfriend is initially a mystery to Class 1A. They start to notice Bakugou acting differently, like being less angry or more distracted. When they finally meet the boyfriend, he could be someone unexpected, like a shy artist type. This would contrast with Bakugou's bold personality. Another plotline could be that the boyfriend is a powerful hero - in - training from another school. Class 1A might be a bit jealous at first but then realize they can learn from him. And there could be a plotline where the relationship is a secret at first and Class 1A accidentally discovers it.
In this fanfiction, Percy's relationship with Paul's family could be complex. There could be some initial distrust from certain family members. However, as Percy shows his good nature and helpfulness, the relationships start to shift. His relationship with Paul would be the foundation, and through that, he builds bonds with the rest of the family. For example, he might help Paul's mother in the kitchen and earn her respect and affection. With Paul's father, he could discuss serious topics and gain his trust.
In a 'Percy Meets Paul' fanfiction, Percy could be a demigod, like in the Percy Jackson series. He has powers related to the Greek gods. Paul, on the other hand, could be a normal human who is very intelligent and curious. Their meeting could be a chance encounter, like Percy accidentally stumbling into Paul's life while on a mission. Or Paul could be someone who has been unknowingly drawn into Percy's world of magic and mystery.
A plotline could revolve around Percy defending his new relationship with Paul to his friends or other family members. Some might not understand why he's so quick to accept Paul as his dad. Also, there could be a plotline where Paul helps Percy through a difficult time, like a school problem or a fight with a bully. This would strengthen their bond and further solidify Percy's decision to call him dad.
I'm not sure of a specific one off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own. There are often a lot of unique crossovers there.
One possible plotline could be a quest. They are both sent on a mission, either by the gods in Percy's world or the deities in Sadie's world, to retrieve a powerful artifact that has been lost between the two mythologies. Along the way, they face many challenges and learn to trust each other.
In such a fanfiction, perhaps there would be an initial confusion. Paul's family might be a bit taken aback by Percy's presence. Percy could show off his demigod skills, like his sword - fighting or water - controlling abilities, which would both amaze and slightly intimidate Paul's family.
Perhaps in 'Percy Meets Paul's Family Fanfiction', Percy enters Paul's family home and is struck by how different it is from his own world. The family has its own set of traditions and values. Percy has to navigate these new surroundings while trying to make a good impression. There might be a family pet that takes an instant liking to Percy or the other way around. As time passes, Percy becomes more comfortable and starts to feel like a part of the family, sharing in their joys and sorrows, and even participating in family disputes as an insider rather than an outsider.
One possible plot is that Percy meets Paul's parents during a family gathering. He feels out of place among all of Paul's relatives. However, he tries his best to be polite and helpful. He helps in the kitchen or with setting up things. Through these small acts, Paul's parents begin to see his good nature. As the gathering progresses, Percy tells some funny stories about Paul that make everyone laugh and he becomes more accepted.
Perhaps in the fanfiction, Paul is in some kind of danger and Bella's choice to be with him is about protecting him. Or it could be that Paul shows Bella a different side of the werewolf world that she finds more appealing than the vampire world she was initially drawn to. It could also involve Bella having to deal with the fallout from choosing Paul, like how it affects her relationships with the Cullens and the other werewolves.