One common trope is the 'against - all - odds' love. Since their relationship is not a typical one in the original series, in fanfiction, they often have to overcome many obstacles like social norms and prejudices. Another is the 'protective - partner' trope. Sirius is very protective of Harry in the original, and this gets amplified in the married relationship fics. They protect each other from various threats, magical or otherwise.
Sure, there are. A lot of fanfiction writers like to play with different pairings and relationships. In the case of Harry and Sirius getting married in fanfiction, it can lead to some really interesting plot developments. For example, they might have to face challenges from the traditional wizarding society which may not be accepting of their relationship. Or it could be a story of them building a new life together, away from all the chaos and danger of the main Harry Potter storyline. It all depends on the creativity of the writer.
In a fanfiction, perhaps there's a magical accident that causes Severus and Sirius to swap bodies for a while. During this time, they are forced to understand each other on a much deeper level. They see the world through each other's eyes and start to appreciate the other's qualities. This new - found understanding leads to a friendship that blossoms into love, and they get married. It could be a story full of humor, as they adjust to each other's quirks while in the wrong bodies.
One reason could be Harry's impulsiveness. Harry often jumps into dangerous situations without thinking, and Sirius, being his godfather and having a protective nature, would shout at him to make him realize the risks. For instance, if Harry decides to go after a Death Eater alone.
Sirius could help Harry cope by sharing his own experiences of being an outcast in his family. He could tell Harry that just because his parents did this horrible thing, it doesn't mean he's unlovable. Sirius could also introduce Harry to his friends in the wizarding world, like Remus, who could also offer support and friendship.
It's possible that in the cave, they start to see each other as equals rather than just a mentor - student relationship. They might argue about the best way to deal with the cave's mysteries at first, but through that process, they learn to value each other's perspectives. Also, if one of them gets injured in the cave, the care and concern shown by the other would enhance their relationship.
Yes, there might be such fanfictions out there. Fanfiction writers often come up with creative and sometimes out - of - the - box ideas. They might explore the idea of Harry having a different relationship to Sirius in an alternate universe where he could be seen as Sirius's daughter. However, it's not a common or traditional take on the Harry Potter universe.
The 'Harry Potter' books are set in a magical world full of its own stories, prophecies, and secrets. Sirius is a complex character with a lot on his plate. He has to deal with his family history, his time in Azkaban, and his loyalty to his friends. Fanfiction is a form of creative writing by fans outside the original story. Sirius doesn't have the time or the inclination within the context of the story to be reading fanfiction. His life is too filled with real magical drama and danger.
One possible plot could be that they got married in secret because of the age difference and the reactions they knew they'd get from the wizarding community. They might keep it a secret by using magic to conceal their relationship, like Sirius using his animagus form to visit Hermione without being detected. And they could be working together on some secret mission that led to their feelings growing stronger.