Maybe Hermione accidentally casts a spell that combines the story of Beauty and the Beast with their world. Harry becomes the 'beast' and Hermione starts to live in the same 'enchanted' area of Hogwarts as him. They gradually develop a deeper understanding of each other. As they explore the magic that binds them in this new situation, they also discover secrets about Hogwarts that were previously unknown.
One idea could be exploring the Beast's past more deeply. Maybe a story about his life before the curse, his relationship with his family and how it all led to his current situation.
One idea could be that Belle discovers a hidden garden in the Beast's castle that has magical plants which can talk and offer her advice. Another could be a backstory for the Beast, like how he got cursed in a more detailed and different way than in the original story. For example, he was tricked by a jealous wizard who wanted the castle for himself.
Maybe the Dark Beauty is not truly human but a being from another dimension. She and the Beast have a connection that transcends their different forms. They must figure out how to break the curse on the Beast's castle while also dealing with her other - dimensional nature.
Well, a cool fanfiction concept could be that Belle discovers a hidden part of the castle that holds the secrets of Beast's past. As she uncovers these secrets, it deepens their relationship even more. Or perhaps a story where Beast gets turned human for a short time and he has to adapt to the human world without Belle by his side at first. He then realizes how much he truly depends on her. Another interesting one would be a fanfiction where Belle's father gets lost in the enchanted forest again, and Beast and Belle have to go on a new adventure to find him.
One idea could be a 'what if' scenario where Gaston has a change of heart. Maybe he realizes Belle's kindness towards the Beast makes her truly special and he tries to make amends for his past behavior. He could start by helping the villagers understand the Beast better instead of leading them to attack the castle.
One interesting plot might be that Gaston somehow gets transported into the enchanted castle with Belle. He then has to learn to live with the enchanted objects and the Beast. This could lead to humorous situations as Gaston tries to assert his dominance in a place where his usual tactics don't work. At the same time, Belle could see a different side of Gaston as he struggles to adapt, and it could change her perception of him too.
Well, a great plot might be that a new character enters the Fairy Tail world who is already under a Beauty and the Beast - like curse. The Fairy Tail members don't initially trust this beast - like person but as time goes on, they discover his good heart. Maybe he has some special power that could help the guild in a future battle, and in the process of working together, the curse is broken.
One idea could be Belle exploring the castle gardens barefoot and discovers a hidden part of the garden that has magical plants. Another could be Belle having a barefoot dance with the Beast in a moonlit ballroom. Or perhaps she goes on a barefoot adventure outside the castle and meets some friendly forest creatures who help her understand the Beast better.
One idea could be that Sebastian from Black Butler gets transported into the world of Beauty and the Beast. He could use his skills to help the Beast court Belle in a more sophisticated way. For example, he might plan elaborate balls or dinners. Another plot could be that Ciel is cursed like the Beast and Belle is a character who is brought in to try and break the curse, but she has some secrets of her own related to the Black Butler universe. Maybe she has a connection to the underworld that Ciel is also involved in.
One idea could be that the Beast has a secret power that he's been hiding from Belle. Maybe he can communicate with the forest animals in a unique way and they help him in his quest to win Belle's true love. Another could be a backstory for the Enchantress who cursed the Beast, showing her reasons and her own journey. Or perhaps Belle discovers a hidden library in the castle that contains the secrets of breaking the curse not just for the Beast but for the entire enchanted castle and its inhabitants.