Perhaps there could be a parallel universe scenario. In this alternate reality, Hermione's role as Lucius' mother could be due to different historical events. It might start with a divergence in the wizarding wars, which results in different pairings and family formations. This could lead to a very different Hogwarts, where Hermione's influence on Lucius shapes his actions towards Muggle - borns and the overall wizarding society in a new light.
For Lucius, his development could be a slow process. At first, he resents being around Hermione, but as he witnesses her magic and her kind heart, he starts to question his own values. He may begin to see the error of his ways regarding blood purity. Hermione might develop more patience. Dealing with Lucius, who has such different views, makes her learn to tolerate and try to change someone rather than just oppose them.
Hermione could also use her magic skills to her advantage. She is a powerful witch, and in the Malfoy household, she may use her magic to create a space for herself where she can be true to herself. She might also use magic to subtly influence Lucius and make him more accepting of her and her beliefs.
One interesting plotline could be the clash of their different ideologies. Hermione, with her strong beliefs in equality and justice, and Lucius, from a traditional pure - blood family with elitist views. Their marriage, forced by the law, might lead to a power struggle within the Malfoy household as Hermione tries to assert her values.
Lucius has a sense of entitlement that comes from his pure - blood upbringing and family wealth. Hermione, being a Muggle - born (in the original story), has had to fight for her place in the wizarding world. So in fanfiction as siblings, Lucius might initially look down on Hermione's more inclusive views, while Hermione would be appalled by Lucius's prejudice. However, as the story progresses, they could learn from each other. Lucius could become more open - minded and Hermione could understand the pressures of a pure - blood family.
The relationship between the Malfoy family and the Weasleys would be very different. Since Hermione is friends with the Weasleys, there could be a strange, new connection between the two families. For example, Draco might grow up with Ron as a sort of family acquaintance, which would change their interactions completely.
In fanfiction, the relationship between Hermione and Lucius can be quite complex. Some fanfictions might explore a scenario where they are enemies forced to work together due to certain circumstances in the wizarding world. For example, they could be paired in a mission to save Hogwarts from a new dark threat. Their different backgrounds, Hermione being a Muggle - born Gryffindor and Lucius a pure - blood Slytherin, would create a lot of tension and interesting character dynamics.
Another idea is that Hermione is there by accident. She could have been exploring the Malfoy Manor (where Lucius's office is located) out of curiosity or in search of something related to Harry Potter's past. Once in the office, she discovers a hidden secret about the Malfoy family that could change the course of the wizarding war.
Fanfiction about Hermione and Lucius can be quite interesting. Writers might play with the concept of redemption for Lucius. Maybe Hermione sees a side of him that others don't. It could also be a way to explore power dynamics in a new context, with Hermione's intelligence and Lucius's former status in the wizarding world.
Well, in fanfiction, this pairing is often a shocker. It's not something you'd expect given their opposing sides in the main 'Harry Potter' plot. But it can be a fascinating exploration of character growth, especially for Lucius who was a rather villainous character.