Another interesting plot could be Nagini's role in the wizarding world if Voldemort had never found her. She was a powerful and intelligent magical being. Maybe she would have become an important figure in the wizarding community on her own, working towards the betterment of magical creatures or something similar. This would show her potential outside of being Voldemort's servant.
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.
A plot that I find very intriguing is when a character travels back in time to prevent the death of a loved one. For example, in some fanfics, Harry travels back to save Sirius. This creates a lot of tension as he has to deal with the time - turner rules and the possible consequences of changing the past.
A really cool plot in some fanfictions is when Nagini has a secret power that even Voldemort doesn't know about. This power could be something that has the potential to change the outcome of the wizarding war. Maybe it's a power that can only be unlocked by a certain person, like Harry, and this creates a whole new set of adventures and challenges.
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.
The plot where Murtagh teaches Harry some of his unique magic techniques is really cool. It shows how different magical systems can interact. For example, in a fanfic I read, Murtagh showed Harry how to use a spell that was common in his world but unheard of in Hogwarts.
In 'The Mysterious Bond between Harry and Grindelwald', the plot focuses on a strange, unspoken bond that seems to exist between the two. This bond affects their decisions and actions throughout the story. It's a unique take on their relationship and makes for a very engaging read.
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.
Well, in some fanfics, like 'The Darker Side of Redemption', Lucius is given a chance at redemption after the fall of Voldemort. Harry plays a key role in this process, either by being a reluctant helper or an unexpected friend. The plot often involves exploring the darker parts of the wizarding world that were not fully shown in the original books.
In some fanfics, the plot might involve Harry using his snake form to spy on the Death Eaters. For example, he could slither into their secret meetings undetected. Another interesting plot could be that his snake form is somehow connected to Salazar Slytherin. Maybe he discovers that his ability to turn into a snake is part of an ancient bloodline magic.
Well, there's a plot where Penelope is secretly a powerful witch with ancient magic in her bloodline. In this fanfic, she has to hide her true power from everyone at Hogwarts. It makes for a really exciting read as she tries to balance her normal school life with the secrets she's keeping.