One idea could be a world where magic is tied to emotions. For example, when a person is extremely happy, they can create beautiful, floating lights. A young girl discovers she has an unusual ability to control negative emotions like anger and turn them into a powerful force to fight against dark creatures that thrive on despair. She has to learn to balance her emotions to use this power effectively.
Another good idea is a story about a magical library. Every book in this library is a portal to a different fantasy realm. The librarian, who is a powerful wizard, has lost the key to the most dangerous book that holds an ancient evil. A novice adventurer stumbles upon the library and must help the librarian find the key before an evil sorcerer does.
One idea could be a story about a lonely lighthouse keeper. He has spent years in isolation, watching the sea. One day, he discovers a strange object washed ashore. This object turns out to be a magical item that starts to change his life and the way he views the world around him.
A fantasy story could be set in a world where dreams are a tangible reality. There are special hunters who go into people's nightmares to slay the monsters that lurk there. The main character is a young trainee hunter who accidentally enters the wrong nightmare and discovers a conspiracy that could destroy the balance between the dream world and the real world. So, they must fight against powerful dream entities to save both worlds.
Imagine a world where people can exchange their dreams. A person who is always dissatisfied with their own dreams decides to trade with others. But they soon realize that each dream has its own problems and that the grass isn't always greener on the other side. Through this experience, they learn to appreciate their own dreams and the unique experiences they bring.
Look at nature for inspiration. For instance, a forest could be a magical place full of fairies and hidden paths. Or a waterfall could be a portal to another world. You can also think about different mythologies and incorporate elements from them, like Greek or Norse mythology.
How about a world where everyone has to wear a device that monitors their thoughts? The slightest hint of dissent and they are immediately sent to 're - education' camps. The main character manages to find a way to disable the device and begins to spread the knowledge of how to do it, creating a subversive movement.
One idea could be a world where people are ranked by their genetic purity. The government controls every aspect of life, and those with 'imperfect' genes are relegated to slums and used for menial labor. The protagonist, a person with a hidden genetic defect, discovers a resistance movement aiming to overthrow this discriminatory regime.
One idea could be a story about a lonely old man who lives in a small cottage on the outskirts of town. On Christmas Eve, he discovers a lost reindeer in his backyard. He takes care of it and in return, the reindeer leads Santa Claus to his cottage, and Santa gives him the best Christmas he's ever had, filled with presents and warm company.
In a dystopian short story, you could have a society where water is extremely scarce. The rich hoard all the clean water, and the poor are left to fight over the little that remains. The main character is a young girl who tries to find a hidden water source that is rumored to exist, facing many dangers along the way. It could show the extreme inequality and desperation in such a world.