One popular 'Nagini pregnant fanfic' might be 'The Unexpected Miracle of Nagini'. It explores the idea of Nagini's pregnancy in a very unique way, with a focus on how the other characters in the Harry Potter universe react to this strange situation.
You need to consider the setting as well. Since Nagini is from the wizarding world, you can incorporate magical elements related to pregnancy. For instance, what kind of magic could be used to take care of her during the pregnancy? Also, think about the reactions of other characters. Will they be horrified, or will some try to use her pregnancy to their advantage? It's all about building a believable and engaging story around this unique concept.
One common theme is redemption. Since Nagini is often seen as a dark creature in the original series, many fanfics explore her journey towards redemption with Harry's help. Another theme is the exploration of the relationship between humans and magical creatures. Harry represents the human side, and Nagini the magical creature, and their interactions can show different aspects of coexistence.
One interesting Nagini fanfic could be one that explores her backstory before she was fully under Voldemort's control. Maybe it delves into her time as a Maledictus, how she coped with her condition, and the choices she made that eventually led her to Voldemort. It could show a more sympathetic side of her.
Some fanfics might explore Nagini's connection to the other Horcruxes. Since she was the last Horcrux to be destroyed, perhaps there was some kind of communication or power exchange between her and the other Horcruxes that we didn't see in the books. This could add a whole new layer of mystery to the story.
Nagini was originally a human woman named Bertha Jorkins. She was cursed and transformed into a snake by Voldemort. Nagini became one of Voldemort's Horcruxes.
A fanfic could also focus on a scenario where Nagini has a change of heart. For example, she could start to resist Voldemort's control due to some unforeseen bond with a character in the Harry Potter universe, like a kind wizard who tries to communicate with her on a deeper level.
It could start with hostility. Harry sees Nagini as a tool of Voldemort, and Nagini is loyal to Voldemort at first. But then, some unexpected events might force them to interact more. For example, they could be trapped together in a magical place, and they have to rely on each other to get out.
You can try fanfiction websites like Archive of Our Own (AO3). There are a large number of Harry Potter fanfics involving Nagini on it. Just use the search function and type in 'Harry Potter Nagini' to find relevant stories.
Nagini was once a human woman. She was a Maledictus, a person cursed from birth. Over time, due to the curse, she gradually transformed into a snake. Eventually, she became one of Voldemort's Horcruxes. This transformation was a long and tragic process, as she lost her humanity bit by bit as the curse took hold.