One plot idea could be a story where the lost girl discovers a hidden realm within the Fae world that holds the key to a long - forgotten power. Another could be a love story between the lost girl and a character who is initially her enemy but then they realize they have a deeper connection. Or perhaps a plot where she has to team up with a group of unlikely allies to defeat a new and powerful threat to the Fae and human worlds.
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.
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.
A love - interest plot for Gideon would also be interesting. He could fall in love with a character from a different realm within the Once Upon a Time universe. Their relationship would be complicated by the different rules and cultures of their respective realms. They would have to overcome many obstacles, like disapproving family members or the threat of war between their two realms.
One idea could be exploring Gothel's backstory before she became the villain we know. Maybe she had a tragic love in her youth that turned her bitter. Another plot could involve Gothel teaming up with an unexpected character from the Once Upon a Time universe, like a hero who thinks they can reform her. A third option is to create a story where Gothel has a daughter of her own and we see how she raises her in contrast to how she treated Rapunzel.
One idea could be to create a story where a new character, an aspiring actress, befriends Rick Dalton and Cliff Booth. She gets involved in their crazy Hollywood adventures and helps Rick revive his career in an unexpected way, like by introducing him to a new type of movie role that suits his acting style better.
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.
Well, a plot could involve time - travel. Henry somehow gets sent back in time to when Regina was first starting to embrace her dark side. He tries to change her path by showing her the future and how she could have a loving relationship with him. Another interesting plot might be that there's a curse on Henry that makes him forget Regina, and Regina has to go through a series of trials to break the curse and make him remember their relationship. Also, they could be on a quest to find a magical artifact that can restore all the good memories of the people in Storybrooke that Regina once took away, and this journey brings them closer together.
One plot idea could be that Gaston has a change of heart after Belle rejects him. He starts to see the error of his ways and tries to become a better person. Maybe he helps Belle with some tasks in the village, gradually winning her respect if not her love.
A possible plot for the Once upon a time Peter and Wendy fanfiction is that an old enemy from Peter's past returns to seek revenge. This enemy targets Wendy because he knows she's important to Peter. Peter then has to use all his skills and the loyalty of his friends in Neverland to protect Wendy. Meanwhile, Wendy shows her courage and intelligence by coming up with her own plans to outwit the enemy. They also have to deal with the fact that some of the Lost Boys are scared of this new threat, and Peter and Wendy have to boost their morale.
One plot idea could be that Hook and Belle team up to find a lost magical artifact. They start off as reluctant partners, Hook being more of a scoundrel and Belle the book - loving intellectual. But as they face various challenges together, like fending off dark magic creatures and solving ancient riddles, they develop a mutual respect. Eventually, they discover that the artifact has the power to rewrite a part of their pasts they both regret.