Yes, there are likely some fanfictions with this concept. Fanfiction writers often come up with creative and alternative family relationships for characters. You can search on popular fanfiction websites like Archive of Our Own or Fanfiction.net using relevant keywords to find such stories.
One great fanfiction could be about Sirius Black's brother's hidden life. Maybe he was involved in some secret mission before his untimely death. Writers might explore his relationship with Sirius in more depth, like the times they spent together as children, their shared secrets and how their paths diverged as they grew older.
Archive of Our Own (AO3) is a great place to start. It has a vast collection of fanfictions, and you can use the search bar to type in keywords like 'Harry Sirius brother'. Another option is Fanfiction.net. Just be sure to adjust the search filters to get the most relevant results.
One common theme is family bonds. Since they are brothers in these fictions, it explores a deeper, more protective family relationship. Another theme is loyalty. Sirius is already known for his loyalty to Harry in the original story, but as brothers, it's intensified. Also, there's often a theme of self - discovery as Harry learns more about his family and himself through this new relationship.
Sure, on Archive of Our Own (AO3), you can discover many 'harry is sirius brother fanfiction'. In these fictions, the authors might rewrite the entire story arc. They could show how Sirius protects Harry in a more brotherly way, and how this new relationship affects Harry's friends and his battles against Voldemort. It's really fascinating to see the different interpretations.
In another fanfiction, Sirius Black's brother was a powerful wizard who had the ability to travel through time. He used this power to try and prevent some of the tragedies that befell his family. This led to some really exciting plot twists as he interacted with different versions of his family members at different times.
Yes, there are likely to be such fanfictions in the vast world of fanfiction. Many fans like to create alternate family relationships and storylines for their favorite characters.
Well, in fanfiction, anything can happen. Just because it says Harry is Uryu's brother doesn't necessarily mean it's going to be a traditional brother relationship. It could be a metaphorical brotherhood, or it could be a result of some crazy plot device like a cross - over between two different universes. So, it really varies from one fanfiction to another.
Sirius would have a big impact on Harry's understanding of family. Harry has always longed for a real family, and Sirius would show him what a loving and supportive family can be like. This would make Harry more open - hearted and less guarded. He would also be more likely to forgive those who have wronged him in the past, as Sirius might teach him the value of forgiveness. Moreover, Sirius' love for adventure could make Harry more adventurous in his exploration of magic and the wizarding world.
I'm not sure specifically as I haven't read this particular fanfiction. But it might involve Sirius learning about Harry's final wishes, perhaps wishes related to his friends, Hogwarts, or the fight against the Dark Arts.