A possible plot is that the lost sister was sent to another dimension by a powerful witch as a means of protecting her from the chaos in the Mikaelson world. In the fanfiction, she grows up in this strange dimension, learning different forms of magic. When she finds a way back to her own world, she meets Hope. Together, they have to face a new enemy that is targeting the Mikaelson family because of their combined power.
One great 'Hope Mikaelson lost sister' fanfiction could be where the lost sister returns and has a special power that helps Hope in her battles against the supernaturals in Mystic Falls. For example, she might have the power to control time, which she uses to undo some of the tragedies that have befallen the Mikaelson family.
One common theme is family loyalty. In many fanfictions, Hope's sister will go to great lengths to protect the family name and her siblings. For example, she might face off against powerful enemies who are threatening the Mikaelsons. Another theme is self - discovery. Since the Mikaelson family is full of complex characters, the sister often has to figure out who she is and what her place is within the family and the supernatural world.
Family loyalty is also a big theme. The twin sister is part of the Mikaelson family, and in many fanfictions, she has to deal with the complex relationships within the family. There could be situations where she has to choose between different family members' wishes or protect the family from a new threat, even if it means sacrificing her own desires.
She might also use her magic. Hope could put protective spells around her sister's living area or on her sister directly. This would make it difficult for enemies to harm her. For example, a spell that alerts Hope whenever someone with malicious intent approaches her sister.
There's also 'Sisterhood in the Shadows'. This fanfic focuses on the bond between Hope and her sister. It shows how they support each other through all the trials and tribulations in the supernatural realm. It has some really heart - warming moments and also some intense action scenes when they face off against their enemies together.
One interesting fanfiction could be where Hope's twin sister has a different power set. For example, while Hope has her typical witch/vampire/werewolf powers, the sister could have the power to manipulate time. In the story, this could lead to all sorts of plot twists as she tries to correct past mistakes in the Mikaelson family's history. Maybe she goes back to when Klaus was first turned into a vampire and tries to prevent it, which would change the entire course of the family's future.
One idea could be a crossover with the Vampire Diaries. Hope could meet Elena and they could form an unlikely alliance against a new threat in Mystic Falls. Maybe a powerful witch from another dimension is causing chaos and their combined powers are needed to stop it.
One great 'Hope Mikaelson Fanfiction' is 'The Ascent of Hope'. It delves into Hope's journey of self - discovery and her struggle with her unique powers. Another interesting one could be 'Hope Among the Shadows' which focuses on her relationships within the Mikaelson family while facing external threats.
The theme of redemption can also be found in some Hope Mikaelson fanfictions. Given the actions of her family in the past, she might be on a journey to make up for some of the wrongdoings associated with the Mikaelson name. And of course, love. There are fanfictions that explore her romantic relationships, whether it's with a new character or someone from the existing universe.