One possible plotline could be Sebastian's struggle with his identity. Having two very different fathers in Snape and Sirius, he might feel torn between their respective legacies. He could inherit Snape's intelligence and Sirius's rebellious spirit. For example, at Hogwarts, he might be sorted into a house that neither of his fathers were in, and have to find his own path within the school while dealing with the expectations that come with his parentage.
One possible plotline could be Snape using his position as master to make Sirius work on a dangerous mission for the greater good of the wizarding world, but Sirius is hesitant at first. Another could be Snape teaching Sirius some long - forgotten or dark magic that Sirius has to master under Snape's strict guidance.
Another plotline could involve Draco's internal struggle. He is raised by Sirius, but still has the influence of his pure - blood Malfoy heritage. This could lead to a conflict within him. He might love and respect Sirius, but also feel the pull of his family's traditional values. This inner turmoil could drive the story as he tries to find his own identity, caught between two very different worlds.
His magic could be a unique blend of Snape's precision and control and Sirius's raw power. For instance, in potions class, he might be able to add a touch of his own magic that has an unexpected but positive effect on the potion, due to Snape's influence. But when it comes to dueling, he could unleash a powerful burst of magic like Sirius, yet with a more calculated approach.
One possible plotline could be Snape finding drunk Harry in the Hogwarts corridors. Snape, being the strict teacher, might initially be angry but then realizes Harry is in a vulnerable state. He could take Harry to his office to sober him up and in the process, they have a conversation that reveals some hidden feelings or understanding between them.
A plotline might involve Sirius and Harry living together and Sirius trying to give Harry a normal family life. He could cook for Harry, help him with his homework, and they could have a pet together. Maybe they get a Kneazle, and Harry learns to take care of it with Sirius' guidance. This would be a contrast to the cold and often neglectful treatment he received from the Dursleys. And as Harry grows, Sirius could introduce him to his old friends like Remus Lupin in a more family - like setting, strengthening Harry's support system.
Well, perhaps in the fanfiction, Sirius would take Hermione on adventures around the wizarding world. Since he was part of the Marauders, he'd know all kinds of hidden places. They could visit ancient magical sites, and along the way, Sirius would share stories about her parents if he knew them. This would not only give Hermione a broader knowledge of the wizarding world but also a sense of connection to her past. Also, he might train her to be a better dueler, preparing her for any threats that come her way in the future.
A plotline could involve a wizard or witch who is actually a descendant of someone related to Sebastian Michaelis. They have some latent abilities or traits that are similar to his, like an uncanny ability to read people. This causes them to stand out in the Harry Potter world and they might face both admiration and suspicion from their peers. They could also use these abilities to solve mysteries or face off against dark wizards in a different way than the typical Hogwarts students.
The sister could have her own love story intertwined with the events of the wizarding world. She might fall in love with a Gryffindor, which would be a huge scandal in the eyes of some. This relationship could be a source of tension, not only within her family but also in the wider wizarding community. And as Severus tries to protect his sister from the dangers of the wizarding war, her relationship could add an extra layer of complexity to his already difficult situation.
Well, a plot could be that Snape adopts Harry due to some unforeseen circumstances. For example, Dumbledore in his infinite wisdom decides that Snape is the best person to protect Harry. Snape initially hates the idea but as he spends time with Harry, he starts to see Lily in him, not just in appearance but in his kind heart. This makes Snape more protective. Harry, for his part, is initially scared of Snape but soon realizes that Snape is actually trying to help him grow into a powerful wizard. They start to have a mutual understanding, and Snape helps Harry with his studies and also with dealing with the trauma of his past.
One possible plotline could be that Snape discovers a hidden weakness of Voldemort. Maybe through his years of spying, he finds out that a certain spell, when combined with an ancient magic artifact, can destroy Voldemort. So he devises a plan to get hold of the artifact and uses the spell at a crucial moment when Voldemort is off - guard, perhaps during a major battle when Voldemort is focused on other opponents.