I'm not entirely sure if there is a specific 'Harry is Gellert sister' fanfic. However, the fanfic community is vast. It could be that someone has created such a story. It might be a very niche or creative take on the characters, perhaps exploring a new family connection or a different kind of magical bond between them. You should start your search on popular fanfic platforms.
You can start by looking on Archive of Our Own (AO3). It has a large collection of Harry Potter fanfics. Just use the search bar and type in relevant keywords like 'Harry Gellert sister' and see what comes up.
Another theme is the exploration of power. Both Harry and Gellert are powerful in different ways. Fanfics often look at how they interact regarding power, like whether they compete or collaborate. For instance, some fanfics have them working together to face a greater threat using their combined powers.
I really like 'Gellert's Influence on Harry'. In this fanfic, Gellert becomes a sort of mentor to Harry. It explores how Gellert's knowledge and experiences shape Harry's views on magic and the wizarding world. The writing style is quite immersive, and the character development is well - paced.
One common theme is the power struggle. Since Grindelwald is a powerful and often controversial figure, fem Harry's relationship with him often involves a negotiation of power, whether it's her trying to resist his influence or finding a way to work with it. For example, in many fanfics, fem Harry might be in a position where she has to use her own unique powers or intelligence to stand up to Grindelwald's grand plans.
There's also 'Fate's Twist' which is really interesting. In this fanfic, fem Harry's character development is intertwined with Grindelwald's. The author does a great job of showing how their encounters change both of them. It delves deep into their personalities and how they interact with the wizarding world around them. The story also has some great plot twists that keep you on the edge of your seat. For example, there are moments where fem Harry has to choose between her loyalty to her friends and her growing fascination with Grindelwald's ideas.
A sense of regret is also common. The idea that things could have been different between them, that they made mistakes that led to their separation or enmity. It's often a sad and poignant theme in these fanfics. And then there's the theme of destiny. Whether their paths were fated to cross and then diverge is explored in different ways.
One great 'albus x gellert fanfic' is 'The Summer of 1899' which delves deep into their relationship during that time. It has beautiful prose and really captures the essence of their connection.
One great 'Harry Potter and Gellert Grindelwald' fanfiction is 'The Redemption of Grindelwald'. It shows a different side of Grindelwald's character, exploring his possible path to redemption. The author does an amazing job of delving into his past and how it could have influenced his actions.
Yes, there are some out there. For example, some fanfictions explore the complex relationship between Harry Potter and Gellert Grindelwald in alternate universes. They might delve into how Harry, with his knowledge of Dumbledore's past with Grindelwald, could be drawn into a different kind of battle against Grindelwald's ideology.