A possible plotline is the girl being hurt by the very magic of Neverland. It could be that the magic has a negative effect on her, causing her pain or making her lose her memories. As the fanfiction progresses, she tries to understand why this is happening and how to reverse it. She might seek help from magical creatures in Neverland or use her own inner strength to overcome the harmful effects of the magic.
One common plotline could be the girl facing emotional hurt from past traumas that are explored within the magical setting of Neverland. Maybe she was betrayed by someone she trusted in Neverland, like a lost boy who turned against her.
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 exploring the backstories of the lost boys in more detail. Maybe one of them has a hidden connection to a character from the outside world. Another plot could involve a new villain coming to Neverland who has a different kind of magic that challenges Peter Pan. Also, a story about Wendy's granddaughter returning to Neverland to find a lost family heirloom could be interesting.
One common theme is the exploration of different mythologies. Both shows have rich mythologies, and in fanfiction, authors often combine or contrast them. For example, the fae lore from 'Lost Girl' and the fairytale magic from 'Once Upon a Time' are often blended to create unique storylines.
One plot idea could be that Captain Hook and Emma Swan find themselves in a race against time in Neverland. They have to retrieve a magical artifact before a dark force uses it to destroy all the realms. Along the way, they face challenges from the Lost Boys and some of Hook's old enemies.
One underrated character is Felix. He's always by Peter Pan's side, but we don't really know much about his past or his motives. Fanfiction could explore his backstory, like maybe he was a lost boy who had a really tough life before coming to Neverland and that's why he's so loyal to Pan. Another could be the mermaids. They are often just seen as minor characters, but they could have their own complex society and relationships that could be delved into in fanfiction.
Another interesting plotline is in 'The Secret Alliance'. Here, Regina and Archie form a secret alliance to uncover a mystery in Storybrooke that no one else is aware of. Their combined skills and knowledge make for an exciting adventure throughout the fanfiction.
One common theme is the exploration of alternate timelines. Since 'twice upon a time' implies a doubling of the story - perhaps one that already exists in the 'once upon a time' framework - fanfiction often delves into how different choices in these two timelines can lead to vastly different outcomes for the characters. Another theme could be the redemption of characters. In these types of fanfictions, characters who might have been villains in the original 'once upon a time' setup could get a second chance in the 'twice upon a time' scenario to change their ways and become heroes or at least more morally ambiguous figures. Also, the theme of lost love and its rekindling is popular. Maybe a couple was separated in the 'once upon a time' but are reunited or have a chance at a new relationship in the 'twice upon a time'.
A 'found family' trope is quite common. Characters who were alone or estranged in the show form a close - knit family in fanfiction. For instance, Henry might bring together different characters who then become his new family. Also, the 'hurt/comfort' trope, where a character is hurt (physically or emotionally) and another character comforts them, is frequently used in Once upon a Time fanfics.
One common theme is time -travel. Since both shows deal with different timelines in some way, fanfictions often explore more about time -travel and how it affects the characters. For example, a character might go back in time to change a crucial event.
Family relationships are a big theme. Some fanfics focus on the family dynamics between characters like the Charmings and their descendants. There are also fanfictions that revolve around the theme of identity. Characters in 'Once upon a time' often have complex identities, and fan writers like to dig deeper into how these identities are formed and how they can change over time.