The mermaids could be the main antagonists. They are known to be jealous and territorial in the Peter Pan stories. If the lost girl catches Peter Pan's attention in a way they don't like, they could make her life in Neverland miserable. They might use their alluring voices and their knowledge of the waters around Neverland to try and drive her away or lead her into danger.
Captain Hook would be a likely main antagonist. He has a long - standing feud with Peter Pan, so he would see Peter Pan's daughter as a target or a way to get revenge on Peter. He might try to capture her or use her to lure Peter Pan out of hiding if he's still alive in the fanfiction's version.
Perhaps an older, forgotten enemy of the Lost Boys could resurface. Maybe someone from their past in Neverland who they thought was defeated but has now returned with a vengeance. This could be a character who was once a Lost Boy himself but turned bad due to some dark influence in Neverland.
One plot idea could be that a lost girl in Neverland discovers she has a special power that can break the eternal youth spell on Peter Pan. Another could be a lost girl forming an alliance with the mermaids to find a way back home against Peter Pan's wishes. And a third could be a lost girl trying to rewrite the rules of Neverland to make it a more equal place for all the lost children.
In some cases, it could be a corrupted lost boy. Maybe one of the lost boys has turned bad due to jealousy or a desire for power. He sees the hurt girl as an easy target to assert his dominance or to gain something from her, like her friendship with Peter Pan. So he becomes the main source of trouble for the girl in the fanfiction.
One idea could be to have Peter Pan meet characters from other parts of the Once Upon a Time realm in a friendly competition. For instance, a race through the magical forests of Neverland against characters like Alice from Wonderland. This would be a fun and exciting story without any inappropriate content.
I really like 'The New Arrival in Neverland'. In this fanfiction, a new character enters Neverland and changes the dynamics between Peter Pan and the other residents. It has some great descriptions of Neverland that make you feel like you're really there. And then there's 'Peter Pan's Hidden Heart'. This one delves into the emotions that Peter Pan tries to hide, which is really interesting as in the show he often comes across as carefree.
The story might involve Belle getting lost in Neverland while searching for a special book that is said to have the power to break all dark curses. Peter Pan finds her and at first, he thinks she's a threat to his rule over Neverland. But as they interact more, he realizes she's not like the villains he's faced before. Belle starts to see the good in Peter, despite his mischievous ways. They could team up to fight against Captain Hook who wants to use Belle's knowledge to find a way to defeat Peter once and for all.
The love interest could be a fairy from a different part of Neverland. Maybe she has a special kind of magic that Peter has never seen before. And this makes him curious and eventually fall in love with her.
A character like a talking tree. This tree could be the guardian of an ancient part of Neverland that has been long forgotten. It could give wisdom and tasks to those who seek its help. Another unique character could be a shadow - weaver. This being can manipulate shadows to create illusions or even trap people within their own shadows. It could add a new level of mystery and danger to the story. Also, a music - making sprite. This sprite can use its music to heal or to cause chaos, depending on the notes it plays.
It could also be a new character, perhaps a dark sorcerer who is jealous of the magic in Neverland. This sorcerer might target Emma because she has an unknown power within her that could disrupt his own plans for the magical world. He would try to separate her from Peter Pan and use her power for his own evil deeds.