Maybe Harry somehow gets transformed into a fawn or has a connection with a fawn. It could be a magical adventure where he has to navigate the world as a fawn or protect the fawn from some sort of danger.
I'm not sure if it's popular. There are so many fanfics out there, and without more information or a broader fan community's input, it's hard to determine its popularity.
I'm not sure specifically as there could be many different interpretations of a 'before the fawn fanfic'. It could be about events that happen prior to the appearance of a fawn in a particular fictional world. Maybe it details the backstory of a character who later encounters a fawn, or it could be about the setting and circumstances that lead up to a fawn - related event in the story.
There's no way to know precisely without reading it. However, it could be that there are human characters if the fanfic is set in a world where humans interact with the fawn. For example, a young child who is curious about the forest and might soon discover the fawn. Or perhaps there are magical creatures other than the fawn that are central to the story before the fawn comes into the picture, like wise old owls or mischievous squirrels.
The plot could involve Harry arriving in Skyrim and being mistaken for a powerful mage. He gets caught up in the political intrigue of the different factions in Skyrim. For instance, the Stormcloaks might try to recruit him because they think his magic can give them an advantage in the civil war. Meanwhile, he's also trying to find a way back to his own world.
Maybe it's about Harry being wrongly accused and his fight to prove his innocence while in jail. He could be making friends with some unlikely characters in the jail who help him in his quest.
Well, it could be that Harry somehow gets transported to Middle - earth and becomes Sauron. Maybe he has to deal with the power and the evil associated with being Sauron while still having some of his Harry Potter traits, like his sense of loyalty and courage, which could create an internal struggle.
The plot could involve Harry being reincarnated as Lelouch. He would bring his sense of justice from the wizarding world. He might use his Parseltongue ability to communicate with the Geass users in a unique way. And he could introduce magic into the Code Geass world, which would completely disrupt the existing power structures. For instance, the Emperor might see Harry's magic as a new threat and try to either control or eliminate him. At the same time, Harry could try to use Lelouch's influence to make the wizarding world more accepting of different species, just as Lelouch was trying to change the world in his own way.
One possibility is that Harry is escaping from some danger in the wizarding world. He boards the ship to get as far away as possible. While on the ship, he discovers that the ship has its own secrets and magic. He gets involved in the ship's internal affairs, like helping the crew deal with a curse that has been plaguing them.
The fanfic could center around Harry's life outside of the main events of the books. For example, it could explore his summer holidays in more detail. He could be spending time in the Muggle world and using his magic in creative ways to solve normal, everyday problems. He might use magic to help his neighbor fix a broken fence without the neighbor realizing it was magic. This would add a new dimension to his character and show how he can adapt his magical abilities to different situations.
One possible plot could be that Hermione and Harry discover a magical cat that has the ability to communicate with them. This cat leads them on an adventure to find a hidden magical artifact. Along the way, they use their knowledge and skills to overcome obstacles.