Well, one possible storyline could be that Percy and his twin witch sister are separated at birth. Percy grows up in the normal world, while his sister is in the magical witch world. Then, through some strange turn of events, they meet. Maybe there's a prophecy about them that brings them together to fight a great evil that threatens both the magical and non - magical worlds.
Perhaps the fanfiction could focus on their relationship. Since they are twins, they might have a telepathic link. The sister could be in trouble in the witch world, and Percy senses it. He then embarks on a journey to save her. Along the way, he discovers more about his own family's history in the magical world and how his sister's powers are intertwined with his own destiny.
If Percy is from a normal world and his sister from the witch world, their worlds could collide when his sister accidentally casts a spell that affects Percy's world. For example, she might be trying to hide from some dark witches and opens a portal that leads to Percy's neighborhood. This sudden appearance of magic in a non - magical place would be a huge collision of their worlds.
Well, perhaps a good plotline would be Percy's twin sister getting kidnapped by a powerful enemy. Percy then has to embark on a dangerous quest to rescue her. Along the way, he discovers more about his sister's hidden strengths and her importance in a prophecy. Or, they could both be sent on separate quests by the gods, but find out that their quests are actually intertwined and they need to work together to succeed in the end.
The character of Percy's twin sister can be developed by giving her unique personality traits. For example, if Percy is brave and impulsive, she could be more cautious and calculating. Her appearance could also be distinct, like having different colored eyes or hair. Additionally, her relationships with other characters in the Percy Jackson universe can help develop her. If she befriends Annabeth, for instance, it can show her intelligence and ability to form strong bonds.
Well, one possibility could be that Elsa's ice powers are related to Haku's water - based abilities in some way. Since they're twins in this fanfiction, maybe they share a common origin for their powers that has something to do with their family or a hidden clan in the Naruto universe. For example, their family could have been exiled from a certain village long ago because of their unique powers, and the story could be about them reuniting and using their powers to face a common enemy.
Well, in the fanfiction, they could have a very close relationship. Maybe they protect each other from the dark forces at Hogwarts. They might share secrets that no one else knows, like about their family's hidden past or their own personal fears and dreams.
Her twin sister could be really outgoing. While Hermione is often seen as a bit reserved in social situations, the sister could be the life of the party. She might be more interested in Quidditch than Hermione and be a great flyer. Also, she could be more impulsive. Hermione thinks things through carefully, but the sister could be the type to jump into action without much planning.
Perhaps the sister gets kidnapped by an enemy of Percy's. Percy then has to embark on a dangerous quest to rescue her. Along the way, he discovers more about his sister's true nature and their family's past that was previously unknown to him. This could involve meeting old friends and making new allies.
It could be an ancient monster that has a grudge against the family of Poseidon. Since Percy and his twin are children of Poseidon, this monster might target them specifically. Maybe it's a sea serpent that was once defeated by Poseidon and now wants revenge by going after his descendants.
One possibility could be that she shows up at Camp Half - Blood unexpectedly. Maybe she was raised by a mortal family all this time, not knowing about her demigod heritage. When she arrives, she has powers similar to Percy's but also some unique ones, like the ability to communicate with sea creatures in a different way than Percy. This could lead to all sorts of adventures and conflicts within the camp as everyone tries to figure out who she really is and what her role will be.
She could be really kind. In contrast to Draco's sometimes haughty attitude, she might be the one who is always helping out the first - years, showing them around Hogwarts and making them feel welcome.