There could be adventures involving the fight against the Dark Arts in a more hands - on way. Sirius would likely train Hermione to defend herself earlier. So, they could be out there hunting down Death Eaters or uncovering Voldemort's early plans. Hermione would use her brains to outwit the enemies, and Sirius would be there to provide the muscle and his own brand of wizarding know - how.
Perhaps they embark on a journey to find a lost magical creature. Hermione would be excited to study the creature, and Sirius would be there to protect them during the search. Along the way, they might encounter other interesting characters or face challenges that test their friendship and abilities.
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.
They could go on a quest to find a lost family heirloom. This heirloom might have special powers that could help in the fight against the dark forces. Along the way, they'd face various challenges like magical creatures and dark wizards.
It would likely make her more self - assured. Sirius would constantly be there to support her and tell her she's capable. This could lead to Hermione being even more outspoken and confident. Instead of just arguing her points in the classroom, she might start challenging the wizarding world's old - fashioned ideas more publicly. Also, she might develop a stronger sense of loyalty to those she cares about, like Sirius, similar to the loyalty he showed to his friends.
In fanfiction, Hermione and Sirius could have a mentor - mentee relationship. Sirius, with his knowledge of the wizarding world and his rebellious nature, could offer Hermione a different perspective on magic and the fight against the dark side. He might share stories of his time in the Order of the Phoenix that would inspire Hermione in her own battles against evil.
She could have adventures with magical farm animals. Maybe there are unicorns in the fields that she befriends and they help her protect the farm from dark magic threats.
She could go on inter - dimensional adventures. For instance, she might help the Justice League travel to different magical dimensions to retrieve powerful artifacts before the villains get their hands on them. Her knowledge of magic would be crucial in navigating these strange and dangerous places.
She could have a very different relationship with Harry. Instead of being just friends, she might be more like an older sister figure, using her family knowledge to guide him. With Ron, their relationship could be more complex. Maybe there would be some jealousy from Ron as Hermione would have a more prestigious family background. And with the other members of the Black family, she would have a family bond. Some of the Black family members who were against Voldemort could be her allies in a more personal way.
Hermione could become more attuned to the darker aspects of magic. With Remus being a werewolf and Sirius having his own dark family history, she might explore the gray areas of magic more. For example, she could study more about the dark arts not to practice them, but to understand how to better defend against them. This would be a significant shift from her canon character who mostly stuck to the 'light' side of magic study.
One possible storyline could be that Bellatrix, despite her dark past, has a change of heart due to some magical influence or a deep - seated love for the Potter family. Sirius, of course, would be a positive influence. They might raise Harry in a more unorthodox way, teaching him both light and dark magic in a balanced way so he can understand the full spectrum. This could lead to Harry being a more powerful and empathetic wizard, able to bridge the gap between different magical factions.