A really interesting plot could be that a curse has been placed on the 'New Girl' world by an angry Greek god. Percy and his friends are the only ones who can break it. The 'New Girl' characters don't believe in magic at first, but as strange things start happening like people turning into animals (à la Greek mythology), they realize they need Percy's help. Percy has to figure out which god placed the curse and why, all while dealing with the quirks of the 'New Girl' characters.
A plot could be that Percy is sent on a quest that leads him to the 'New Girl' universe. He has to find a magical item hidden in the loft. The 'New Girl' characters think he's crazy at first, but as they see the magic unfold, they help him. Another plot could be that one of the 'New Girl' characters discovers they are a demigod. Jess, for instance, realizes she has demigod powers and Percy has to train her. This would bring a whole new dynamic to the loft as she tries to balance her normal life and her new demigod life.
One of the best plots might be a time - travel scenario. The 'New Girl' gang travels back in time to the era of the Greek gods. They meet a young Percy Jackson (or his ancestors) and get involved in a prophecy. They have to use their modern - day knowledge and skills along with Percy's help to fulfill the prophecy. Or, a plot where the demigods need to blend in with the 'New Girl' characters to hide from a powerful enemy. They end up learning a lot about human relationships from the 'New Girl' gang in the process.
One idea could be that the new girl is a demigod from a very rare and powerful lineage. For example, she could be a descendant of a primordial god that no one has seen in centuries. This would bring a whole new dynamic to Camp Half - Blood as everyone tries to figure out her powers and where she fits in.
She could be the daughter of a minor god that hasn't been introduced much in the original Percy Jackson series. For instance, the daughter of Hecate. This would give her powers related to magic, which would be really cool in the context of the story. She could use her magic to help Percy and his friends in battles or to solve some of the mysteries they encounter.
There could be a plot where the girls in the fanfiction are having a girl talk about the strange creatures they've encountered in the Percy Jackson universe. They might be swapping stories about the first time they saw a centaur or a satyr. They could also be discussing their strategies for dealing with the more dangerous creatures, like the minotaurs. This kind of girl talk not only shows their friendship but also their growth as demigods.
There's a character in some fanfictions called Nova. She's a really interesting girl character. Nova is a daughter of Hecate, and she has powerful magic abilities. She often uses her magic to get the demigods out of tricky situations. Then there's Eira, a daughter of Poseidon in some fanfictions. She has the ability to control water in a unique way, different from Percy. She's strong - willed and is not afraid to stand up for what she believes in. Also, many fanfictions feature a girl named Thalia, who is already a well - known character from the original series but is often given more depth and new storylines in fanfiction.
One interesting crossover could be Percy Jackson finding himself in the world of 'New Girl'. He might use his demigod skills to solve the zany roommate problems. For example, when Nick and Schmidt have one of their epic arguments, Percy could use his water powers to cool them down, literally. Maybe he'd also introduce the 'New Girl' characters to some of his demigod friends like Annabeth, and they'd all go on adventures in Los Angeles together.
One interesting crossover could be a scenario where Jess from New Girl somehow stumbles into the world of Percy Jackson. Maybe she thinks it's all part of some elaborate prank at first. For example, she could meet Percy and mistake his sword for a prop. Percy would be confused by her modern and rather eccentric behavior. Another idea could be that the loft in New Girl becomes a haven for demigods on the run. They use it as a hiding place and Jess and the gang have to deal with all the chaos that comes with having demigods around, like strange monsters showing up or magical items causing havoc in the loft.
Well, the new girl could be a demigod who doesn't know her true identity at first. She might arrive at Camp Half - Blood and start to show extraordinary powers. Maybe she has a special connection to Percy Jackson, like they share a common enemy that they have to face together. This could lead to an exciting adventure filled with battles against mythical creatures and the discovery of her own past.
She could be really shy at first. Maybe she comes from a place where she was always bullied for being different, so when she arrives at Camp Half - Blood, she has a hard time opening up to others. But as she discovers her powers and makes friends, she slowly becomes more confident.
Well, in my opinion, the best Percy Jackson fanfictions are the ones that continue the story after the main series ends. They give us more adventures for Percy and his friends. Also, fanfictions that rewrite certain events in the original story in a creative way can be really good. For instance, if the Battle of Manhattan had a different outcome. And fanfictions that focus on the relationships between the characters, like the friendship between Percy and Grover, are always enjoyable.
Well, it's hard to say which one is the absolute best. But some popular ones have great character development and stick closely to the original world-building.