A great plot idea would be that when they time travel, they accidentally change something in the past that has a huge ripple effect on the future. They then have to figure out a way to fix it. Maybe they make it so that Sirius was never disowned by his family in the past, which changes his whole life trajectory. This could lead to a completely different future for the wizarding world, and they have to race against time (again) to make sure the future doesn't go completely haywire.
One interesting plot could be Hermione and Sirius traveling back in time to prevent a certain dark wizard from rising to power. They could use their combined knowledge and skills to subtly change events. For example, Hermione's knowledge of magic history and Sirius' experience in the wizarding world could help them figure out how to stop the dark wizard's early supporters.
A possible plot is that Hermione discovers some long - lost secrets about her father, Sirius. This could lead her on a quest to uncover the truth about his past and his family. Along the way, she might find out about some hidden magical artifacts or spells that were associated with Sirius's family line. It could also involve her interacting with Sirius's old friends and enemies, which would create a lot of interesting dynamics. For instance, she might have to deal with some who are still bitter about Sirius or others who want to protect his legacy through her.
One plot idea could be Hermione discovering her true parentage through a series of magical events. Maybe she stumbles upon an old family heirloom that has a connection to Sirius. Another could be her having to deal with the reactions of her friends, like Harry and Ron, who are shocked by this revelation. She might also face challenges within the wizarding community as Sirius had a somewhat controversial past.
One idea could be that the daughter inherits Hermione's intelligence and Sirius's rebellious spirit. She might use her smarts to uncover secrets about the wizarding world that were long buried, like hidden spells or lost histories. Another plot could involve her struggling to fit in at Hogwarts, being the daughter of two such well - known figures. She could face both envy and admiration from her peers.
Another plot could be set in an alternate universe where Sirius never went to Azkaban. He and Hermione meet when she is a young, brilliant witch just starting at Hogwarts. Sirius, being a bit of a rebel, takes Hermione under his wing and they embark on adventures outside of the school rules, exploring the Forbidden Forest together and uncovering secrets about the wizarding world that are not taught in classes.
One idea could be that Hermione travels back in time and accidentally gets involved with Lucius in his Hogwarts days. Maybe she has to work with him to prevent a dark magic event that would have far - reaching consequences in the future. This could lead to a strange alliance where they start to see each other in a different light.
One idea could be that Hermione and Bill travel back in time to the founding of Hogwarts. They could witness the four founders making their decisions about the school, and Hermione, with her vast knowledge, might accidentally influence some of their choices. For example, she could suggest a different way of sorting students that gets incorporated into the Sorting Hat's initial magic.
One idea could be that Hermione travels back in time and accidentally changes something that affects James's future. Maybe she saves someone important to James that was supposed to die, and then they have to deal with the altered timeline together.
One plot idea could be that Hermione and Rodolphus travel back to the time when the Hogwarts founders were alive. Hermione could use her knowledge to try and influence the early magical laws and education system. Meanwhile, Rodolphus, being from a different era, would have a hard time adjusting and his dark magic - influenced mindset might create conflicts. For example, he might try to introduce some of the more extreme pure - blood ideologies which Hermione would vehemently oppose.
Perhaps the soul bond is a key to a hidden magic. They discover that together they can unlock ancient spells or access a secret part of the wizarding world. They then have to go on a quest to figure out what this all means and how it relates to the greater good of the wizarding community. It could involve facing many challenges and relying on their unique bond to get through them.