In this type of fanfiction, it might be that Sirius Black spanks Harry as a reaction to Harry making a hasty decision that could have had far - reaching negative consequences for himself or others. It could be part of a larger story arc where Harry then has to learn from this experience and grow as a character.
One possible scenario could be that Sirius Black spanks Harry as a form of discipline for some dangerous or disobedient behavior that Harry has engaged in within the context of the fanfiction's plot.
Perhaps in the fanfiction, Sirius Black spanks Harry because he feels that Harry has put himself in unnecessary danger, like sneaking out to face a dark wizard alone. It could be a way for Sirius to show his concern and also teach Harry a lesson about safety and following the rules set by those who care about him.
One possible plotline could be that Harry has done something dangerous in the wizarding world, like sneaking into the Forbidden Forest without permission. Sirius, as his godfather, decides to give him a mild spanking as a form of discipline while also explaining why his actions were wrong and how they could have put him in great danger.
It might also be a situation where Sirius is frustrated with Harry for doing something reckless. He pins Harry down to get him to listen and understand the seriousness of his actions. For example, if Harry was planning to go after a powerful enemy alone without a proper plan.
One possible theme could be discipline within their friendship. Maybe in the context of the fanfiction, Sirius has done something that James feels requires a form of reprimand in this rather unorthodox way.
It could develop in a complex way. The spanking incident might initially create tension between them. Harry could be angry or resentful towards Sirius at first.
Perhaps in the fanfiction, Sirius gets involved with the wrong crowd. And Harry, who has a strong sense of right and wrong, can't stand being associated with Sirius any longer. Or maybe Sirius has a falling out with one of Harry's other important people, like Hermione or Ron, and Harry takes their side and starts to hate Sirius as a result.
Yes, there might be some fanfiction with this theme that is written in a non - offensive and family - friendly way. It could focus on Sirius Black disciplining Harry Potter in a more light - hearted or mentoring - type of situation rather than anything inappropriate.
I'm not entirely sure specifically what that particular fanfic is about as there could be many interpretations. It might be a story where Sirius has some sort of disciplinary or perhaps an unexpected interaction with Harry within the context of fan - created Harry Potter lore.
One possible reason could be a misunderstanding. Maybe some false information was spread about Harry that made Sirius believe he had done something unforgivable. For example, if there were rumors that Harry was involved with dark magic in some way, Sirius, who has a strong aversion to the dark side, might be quick to disown him.
Maybe Sirius wants to train Harry himself. In fanfiction, he could believe that he has a better understanding of the Dark Arts and how to fight Voldemort compared to the professors at Hogwarts. So, he kidnaps Harry to start his own special training regime away from the school.
In some fanfictions, it could be due to dark magic influence. A spell or a dark force might have corrupted Sirius's mind, making him turn against Harry.