In a fanfiction scenario, it could be that Bellatrix has a change of heart after being exposed to Harry's unwavering goodness over a long period. This slow transformation could lead to an unexpected romantic relationship. Their baby could then be a symbol of hope in a world that is divided between the light and the dark. The baby could have unique magical abilities, being the product of two very different magical heritages.
One way could be through a time - travel or alternate reality plot device. Maybe in a world where dark and light magic collide in unexpected ways, Harry and Bellatrix are forced to work together and somehow, against all odds, a connection forms that leads to a child. It would be a very complex relationship, full of inner turmoil for both characters.
One way could be through a magical mix - up. Maybe a dark wizard, in an attempt to control Harry or Bellatrix, forges a marriage contract long forgotten. Harry, upon discovering it, might initially be horrified as Bellatrix is a Death Eater. But as the story progresses, he could see it as a way to infiltrate the Death Eaters from the inside. Bellatrix, on the other hand, might see Harry as a powerful asset. So the plot could develop with a lot of power plays and mind games between them.
Well, it could add a really strange and unexpected dynamic to the plot. It might make the story more about Bellatrix's warped sense of power and control. Maybe she's using this 'baby - like' treatment to manipulate Harry in some way, like trying to break his spirit more easily by infantilizing him.
Maybe she wants to humiliate him. By treating him like a baby, she can make him seem weak and powerless.
I'm not sure if there is such a specific fanfiction. It's a rather unusual and probably not very common concept within the fanfiction world. The general fanfiction often focuses on more mainstream relationships and storylines in the Harry Potter universe.
You can also show her doubts. Even though she was a loyal Death Eater, there could be moments where she questioned Voldemort's methods or decisions. This would make her more human and less of a one - dimensional villain.
The key is to focus on the relationship development. For example, if Harry is kidnapped by a family, show how he and the other character interact from a young age. Maybe they start as friends and then slowly realize their deeper feelings. Also, add some mystery about his true identity which adds tension to the romance.
One possible plot could be that Bellatrix, in a strange turn of events, decides to train Harry in the Dark Arts not to turn him evil but to make him a more formidable opponent against Voldemort. She might see his potential and think that by teaching him some of the Dark Arts, he can better understand Voldemort's tactics.
One possible plot could be that Harry discovers a powerful and dark magic spell that allows him to gain control over Bellatrix. He then uses this to his advantage to gather information about Voldemort's plans from her. Harry might struggle with the moral implications of enslaving someone, even a Death Eater like Bellatrix.
In a 'harry is the son of bellatrix' fanfiction, the plot could be quite complex. Maybe Bellatrix was under a spell when she had Harry, and she doesn't remember it. Harry, on the other hand, is raised by the Dursleys as usual, but strange things start to happen. He has an unusual connection to Bellatrix's magic. As he enters Hogwarts, he discovers the truth through some magical object or encounter. This leads to a whole new set of challenges. He has to deal with the fact that his mother is a known Death Eater, and he may be ostracized. At the same time, he might have to fight against the dark forces within him that are influenced by Bellatrix's heritage while trying to use his new - found knowledge to save the wizarding world in a different way than in the original story.
There would also be challenges in terms of the baby's protection. Both the Order of the Phoenix and the remaining Death Eaters could see the baby as a threat or a tool. The Order might fear that the baby could be turned to the dark side, while the Death Eaters might want to use the baby's power for their own evil purposes. Harry and Bellatrix would have to constantly be on guard to protect their child.