One possible fanfiction could involve Bellatrix going back in time to try and change the outcome of the Battle of Hogwarts in her favor. Maybe she uses time - turners or some dark magic to travel back. She could attempt to kill Harry Potter as a baby before he even becomes a threat.
One common theme is redemption. Sometimes Bellatrix is given a chance at redemption through the time - travel aspect, like she might see things differently and change her ways. Another theme is the power of knowledge. Harry, with his knowledge from the future, has to figure out how to use it in the past to deal with Bellatrix and the challenges of that time.
Another theme is the exploration of the characters' psyches. Bellatrix is a complex and often deranged character. When Harry time - travels and interacts with her, it gives the author a chance to dig deeper into what makes her tick. We see her in a different light, and Harry also has to reevaluate his own understanding of good and evil. This can lead to some very interesting character development throughout the fanfiction.
One popular 'Harry and Bellatrix time travel fanfiction' is 'A Twist in Time'. It has an interesting plot where Harry somehow gets sent back in time and has to deal with Bellatrix in a whole new way.
There's 'Back Through Time with Harry and Bellatrix'. It delves into how Harry's knowledge of the future affects his interactions with Bellatrix during his time - travel adventure. The author does a great job of building suspense and changing the original narrative in interesting ways.
In a time - travel Bellatrix fanfic, she might go back to the time when she was first introduced to the Dark Arts. This could show a different side of her, perhaps a more innocent - looking but still dark - inclined Bellatrix. She could interact with younger versions of other Death Eaters and form different alliances that change the course of the future in the wizarding world.
She could travel back to the time when Voldemort was still in hiding as a young Tom Riddle. Bellatrix might try to influence him in a different way, perhaps making him even more ruthless. This would change the course of the wizarding world in a very different direction.
In a time travel scenario, their relationship could become a complex love - hate relationship. Bellatrix may find herself attracted to Harry's courage and determination in a different way than she's used to. Harry, while disgusted by Bellatrix's actions in the original timeline, may start to see a different side of her when they are in a different time period. This would be a very strange and morally ambiguous relationship, full of internal and external conflicts.
One common theme is redemption. In many of these fanfics, Harry tries to redeem Bellatrix by changing her past. For example, in some stories, he shows her the error of her ways by taking her to see the future consequences of her actions.
Bellatrix Black, in a fit of desperation to change the outcome of the Battle of Hogwarts for the Death Eaters, stumbled upon a time - travel spell. She traveled back to the time when Harry Potter first arrived at Hogwarts. She planned to kill him right away, but she was thwarted by Dumbledore, who seemed to sense something amiss. Dumbledore, with his great power, managed to trap Bellatrix in a time - loop for a while until she finally managed to break free. But by then, she had missed her chance to harm Harry and had to return to her own time, realizing that time itself was a powerful force that couldn't be easily manipulated.