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.
Another interesting plot could be a time - travel fanfic where a character from the present in the Harry Potter world goes back in time and tries to prevent Nagini from becoming a Horcrux. This would involve a lot of interaction with the past versions of characters and a race against time to change the course of Nagini's fate.
Another plot could be set in an alternate universe where Nagini has a different origin. Maybe she was an ordinary snake that was experimented on by dark wizards, and Harry stumbles upon her during his travels. He then decides to help her break free from the dark magic that binds her, and in the process, they form an unlikely bond. This bond could then be tested as they face various threats from both the wizarding world and those who want to use Nagini for their own evil purposes.
One interesting 'Harry Potter Nagini' fanfiction could be about Nagini's backstory before she was Voldemort's snake. It might explore how she came to be an Animagus in the first place. Another could be a story where Nagini has a change of heart and decides to help the Order of the Phoenix against Voldemort. There are also fanfictions that focus on the relationship between Nagini and other characters like Snape, imagining how they might interact in different scenarios.
Perhaps in this fanfiction, Nagini has a hidden past that is related to Harry's family. For example, she could have been an experiment of some dark wizard long ago that was somehow connected to Harry's ancestors, and this discovery leads to a complex relationship between Harry and Nagini as they try to uncover the truth.
Well, you could have a fanfic where Voldemort uses DND - style dark magic to open portals to other dimensions. The Order of the Phoenix has to quickly learn DND - style combat and magic rules to fight off the new threats that come through these portals. Harry could be sent on a special mission to find a DND - style mage who can teach them the counter - spells. Meanwhile, the Death Eaters are also trying to master this new form of magic for their own evil purposes. This would create a really exciting and unique story.
Perhaps a plot where the protagonist can choose to either side with the Ministry of Magic during a time of political unrest within the wizarding world or join a rebel group. This would involve different magical battles and moral dilemmas depending on the choice. In the 'harry potter cyoa fanfic', this could show different aspects of the wizarding society that we don't often see in the original books.
A cool plot for a Harry Potter Twilight fanfic could be a competition. The wizards from Harry Potter and the vampires and werewolves from Twilight compete in a series of challenges. These challenges could test both magic and the unique abilities of the Twilight characters. Or perhaps a love triangle between a Harry Potter character, a Twilight vampire, and a Twilight werewolf. It would be interesting to see how the different cultures and powers interact in matters of the heart.
Another plot could focus on the lives of the secondary characters from the original series. For example, Neville could be the head of Herbology at Hogwarts and discovers a new, dangerous plant that has some sort of connection to an ancient magic. The 'carry on fanfic' could then be about how he and his students deal with it, with some cameos from the main characters.
One idea could be that a dragon escapes from Gringotts and Harry has to use his skills to track it down. Maybe the dragon has a special connection to a powerful dark magic item that Voldemort was after.
One idea could be that Voldemort somehow enters the Runescape world to seek more power. Harry and his friends follow him there to stop him. They have to learn the rules of Runescape quickly to be able to fight Voldemort. Another idea is that a Runescape wizard discovers a portal to the Harry Potter world and brings some of the unique items from Runescape, like special runes, which causes a stir in the wizarding world.
A great plot for a Harry Potter academy fanfic might be a time - travel scenario. A group of students accidentally travel back in time to the founding days of Hogwarts. They have to navigate the different rules and attitudes of that era while also trying not to change history too much. Or perhaps there's a plot where a student is wrongly accused of a major crime at the academy and has to prove their innocence. They'll need to use their wits and the help of their friends to find the real culprit.