It affects Harry greatly. Harry has always longed for a family connection, and Sirius coming back during Christmas gives him that. He now has someone who truly cares for him like family during the festive time. For Hermione and Ron, it means more protection for their friend Harry. They also get to see a side of Sirius that is more at peace during Christmas, which might change their perception of him.
For Remus Lupin, Sirius' return at Christmas is bittersweet. They have a long - complicated history. It brings back old memories, both good and bad. But overall, it strengthens their bond again. The Weasley family might welcome Sirius with open arms during Christmas. They are a big family full of love, and Sirius' presence adds to the warm and chaotic Christmas atmosphere at the Burrow. And Dumbledore, he might see Sirius' return during Christmas as a sign of hope for the fight against Voldemort, as Sirius can be a great asset.
One common theme is redemption. Sirius has been through a lot, and in Christmas - themed fanfictions, he might find a chance to redeem himself in the eyes of the wizarding world or his friends. Another theme could be family. Christmas is a time for family, and Sirius, who has lost his family in a way, may find a new family among his friends like Harry and the others at Hogwarts. Also, the theme of hope often appears. With the magic of Christmas, there's hope for a better future for Sirius, away from his past troubles.
Definitely Hagrid. Hagrid has always been around Hogwarts and has a connection to the students. Sirius could interact with Hagrid if he goes back in time. Maybe Hagrid could help Sirius in some way, like providing shelter or information. And Bellatrix Lestrange could also be in the picture. Since she is part of the Black family, Sirius might have to deal with her in the past, either to try to change her or to stop her from doing something evil.
Sirius would be shocked at first. He had grieved for his brother, so his return would bring a mix of emotions like anger for being left in the dark and joy at having his brother back. Their relationship would be complex as they'd have to deal with the past. Sirius might also be a bit jealous if Regulus was getting more attention or if he seemed to have a better plan against Voldemort.
This event in the fanfiction could potentially change the dynamics of all three characters' relationships completely. Snape might start to view Sirius in a different light, perhaps seeing him as more reckless and dangerous for revealing such a big secret. Remus could feel betrayed by Sirius and start to distance himself. And Sirius might find himself in a difficult position, having to deal with the consequences of his actions and trying to repair the relationships he has damaged with both Remus and Snape.
It could enhance their relationship if the fanfiction gives Harry new topics to talk about. For example, if the fanfiction is about a magical adventure similar to their own experiences, they can bond over it.
It can strain their relationship. If the argument is really intense, they might not trust each other as much immediately afterwards. For example, Harry might start to question Sirius' motives and Sirius could feel that Harry doesn't respect his experience.
It can add tension. Sirius is an important character, and Hermione being rude to him can create a divide among the characters. This divide can drive the plot as other characters might have to choose sides or try to reconcile them.
The main difference is the focus on abuse. While other fanfictions might focus on his heroics or his relationships in a more positive light, 'sirius black abused fanfiction' delves into the darker side of his character. It might show aspects of him that are not so pleasant and explore the consequences of those actions.
If Sirius hits Harry, it can initially strain their relationship. Harry may feel hurt and confused, especially if he trusts Sirius. It could lead to a period of estrangement.
Obviously, Harry Potter and Sirius Black are the main characters. Harry is the time - traveler, and Sirius becomes his mate in this new timeline. Other characters like Dumbledore are likely to also play important roles, as he is always involved in matters related to Harry and the greater good of the wizarding world.