For Belle, emphasize her love for knowledge as an orphan. Maybe she was left with only a few books from her parents, and that sparked her thirst for learning. She could be shy at first but becomes more confident as she and Anna face challenges. For Anna, highlight her adventurous spirit which could be a result of growing up without parents and having to fend for herself. She's always eager to explore new things.
One idea could be that Belle and Anna, both orphans, meet in a magical forest. They discover they have a shared ability to communicate with forest spirits. Together, they embark on a journey to find a hidden library that is said to hold the secrets of their pasts. Along the way, they face challenges from an evil sorcerer who wants to stop them from reaching the library.
Elsa would be a great character to pair with them. Given her relationship with Anna in the original story, and her ice powers could add an interesting dynamic to any story with Belle. They could all work together to save a frozen kingdom or something similar.
One interesting fanfiction could be about Belle and Anna becoming best friends in the 'Once Upon a Time' universe. They might go on adventures together, helping each other out with their respective problems. For example, Belle could use her knowledge of books to assist Anna in understanding some ancient magic that she comes across.
To develop their characters, start with their backstories. For Ella, you could think about her family. Maybe she comes from a poor family but has big dreams. For Thomas, perhaps he is from a noble family but feels trapped by the expectations. This can shape their personalities and goals.
Peter Pan might initially see Belle as a potential addition to his Lost Boys. But Belle has her own ideas and goals. She would resist his attempts to make her part of his group. However, as they spend more time together, they start to see the value in each other. Belle might use her intelligence to help Peter with some problems in Neverland, like a shortage of food or a threat from a new magical creature. Peter would use his flying skills to take Belle to places she needs to go for her own quests. Their characters would interact in a way that challenges each other's beliefs and helps them both grow.
Hook's character can be developed through his relationship with Belle. He could start to value things like knowledge and kindness more as he spends time with her. He might even start to read books under her influence! Belle, on the other hand, could become more worldly. Hook could introduce her to the rougher side of life outside of her castle and library, and she could learn to adapt and use that knowledge to help others in different situations.
In this fanfiction, Belle could convince Rumpelstiltskin to leave his life of dark magic behind. She shows him the beauty of a simple life, away from all the deals and power - hungry individuals. They could move to a small village and start anew, with Rumpelstiltskin using his skills for good, like making beautiful fabrics for the villagers.
In a fanfiction, Belle and Rumpelstiltskin could go on an adventure outside the Dark Castle. They encounter a powerful sorcerer who wants to steal Rumpelstiltskin's magic. Belle uses her wits to outsmart the sorcerer while Rumpelstiltskin uses his magic to protect them both. This adventure could strengthen their bond and lead to a new understanding between them.
Well, adventure is a big theme. Anna is usually put in some sort of exciting adventure in the fanfictions, like exploring new lands or facing dangerous enemies. Magic is another theme. Given that 'Once Upon a Time' is full of magic, fanfictions often involve Anna dealing with different types of magic, either learning new spells or fighting against dark magic. And of course, there's the theme of good vs. evil, with Anna usually on the side of good.
To develop the characters more deeply, give them internal conflicts. For instance, Rick could be constantly battling his insecurities about his acting skills despite his success. And Cliff could struggle with his violent tendencies, trying to control them in a world that sometimes demands his aggression. You could also show their dreams and fears. Rick might be afraid of losing his fame completely, and Cliff might dream of a more stable life but feels he can't leave Rick's side.