Well, often there's the plot of Hermione being the one to see something in Bellatrix that others don't. So she might start a relationship with her that gradually turns into marriage. There could be a lot of conflict with the Order of the Phoenix who would be against Hermione's relationship with a former Death Eater. And Bellatrix might have to face her past actions and make amends in some way as part of the relationship development.
One key plot point could be Bellatrix's initial motives for taking Hermione under her wing. Maybe she sees potential in Hermione's magic and wants to corrupt it for her own dark purposes. Another aspect could be Hermione's struggle to maintain her own values while being in Bellatrix's influence. For example, she might resist Bellatrix's attempts to make her use dark magic. Also, the relationship between the two characters would be complex, with Bellatrix being a cruel and unpredictable mentor, and Hermione constantly trying to outwit her in some way.
Well, in this fanfiction, perhaps there's a time - travel element. Hermione goes back in time and somehow gets involved with Bellatrix in a way that changes their relationship. Bellatrix might be less extreme in her younger days, and Hermione's modern ideas influence her. This could lead to a relationship that blossoms into marriage over time.
A Hermione and Bellatrix married fanfiction could also take a more magical - realism approach. There could be a magical bond that forms between them against all odds. This bond could be the result of a powerful spell gone wrong or a mysterious prophecy. Their marriage would then be a journey of discovery, not just of each other, but also of the implications of their union on the wizarding community. It might face a lot of opposition from both sides, but they could fight for their love, with Hermione using her logic and Bellatrix her fierceness.
Often, there's a focus on how they decorate their new home together as a married couple. This can be really detailed, like choosing the right magical wards for the nursery when Hermione is pregnant. And then there are the challenges they face in their jobs. Harry might be an Auror and have to balance his dangerous job with protecting his pregnant wife, Hermione, who could be working on some important magical research project at the same time.
One common plot device is the use of mind control or dark magic spells on Hermione. This forces her into the slave role. Another is the idea of Bellatrix using Hermione to get to Harry or the other members of the Order. Sometimes, there's a focus on Hermione's inner strength as she tries to break free from the slavery, which is also a plot device to create tension and drama.
Survival is a prevalent theme. Given Bellatrix's murderous and unpredictable nature, Hermione often has to fight for her survival in these fanfictions. It could be a physical fight, or a mental battle as she tries to outmaneuver Bellatrix in a dangerous situation.
A common theme is power struggle. Bellatrix is a powerful and dark witch, and Hermione is also very powerful in her own way with her intelligence and magic skills. So, there's often a back - and - forth as they try to assert their influence over situations or each other.
One possible plot could be that Bellatrix captures Hermione and tries to torture her for information about Harry. But Hermione, using her wits and some new-found powerful magic she has been secretly studying, manages to turn the tables and kill Bellatrix in self - defense.
Yes, it's a somewhat common plot in some fanfiction. Many fans like to explore alternative relationships in the Harry Potter universe, and Hermione and Harry have a strong friendship in the original series, so some writers take it a step further and have them secretly marry in their stories.
Redemption is also a theme. There are fanfictions where Bellatrix has a chance at redemption through her relationship with Hermione. Maybe Hermione sees something in Bellatrix that others don't and tries to bring out the good in her. It's an interesting way to explore the character of Bellatrix beyond her villainous role in the original books.