A really unique plot twist can be found in 'The School that Changed Natsu'. Here, the school Natsu attends is actually a magical illusion created by an enemy. The whole school experience is a trap to keep Natsu and his friends away from Fairy Tail during a crucial time. Natsu has to figure out the truth and break free from this false reality, which leads to some intense and exciting scenes.
One possible plot twist could be that Lucy initially refuses Natsu's proposal because she fears it will change their dynamic in the guild. She might think that getting married will make them less focused on their adventures and more on domestic life.
A great plot twist could be that Natsu loses his magic power right before a crucial match in the Grand Magic Games. But then he discovers a hidden reserve of power within himself, perhaps related to his past or his dragon heritage. This new power allows him to come back stronger and win the match in an unexpected way.
Another plot twist could be the revelation of a hidden connection between Natsu's dual dragon slayer powers and an ancient prophecy. Maybe it was foretold that a dual dragon slayer would be the key to saving the world from a great evil, but also that this same person could bring about destruction if not guided properly. This would add a lot of moral and ethical dilemmas for Natsu and his friends.
A good plot twist could be that Natsu's Fire God Slayer magic is actually a curse in disguise. It was given to him by an evil entity that wants to use him for its own purposes. This would completely change the direction of the story and add a lot of mystery.
Another plot could revolve around Natsu being the new kid at school and having to earn the respect of his classmates. He gets into various battles and challenges, not just physical ones but also magical duels of wits. His friends from Fairy Tail might visit the school from time to time to help him out or just to see how he's doing. And as he overcomes these challenges one by one, he gradually becomes a respected and feared figure at the school, all while still maintaining his fun - loving and loyal nature.
One unique plot point could be Natsu having to learn magic in a completely different way under Mavis' tutelage. Instead of his usual hands - on, instinctive approach, he has to study theory and history. Another could be Mavis using Natsu to revive some long - lost traditions of the Fairy Tail guild. Maybe Natsu discovers a hidden power within himself that was dormant until Mavis guided him.
One possible plot twist could be that Zeref actually doesn't want to fight Natsu seriously and has some hidden agenda. Another could be that Natsu discovers a new power during the fight that is related to his past or his true identity.
One unique plotline is where Juvia and Natsu accidentally swap magic powers. This leads to a lot of chaos as Juvia tries to control Natsu's fire magic and Natsu struggles with Juvia's water magic. They have to learn to adapt quickly to this new situation while also dealing with the threats that come their way.
One possible plot twist could be that Natsu's one - arm state makes him struggle with his magic at first. But this leads to him discovering a new, more powerful and unique form of his magic that he wouldn't have found otherwise. For example, he might have to rely more on his fire control skills rather than brute strength in battles.
One idea could be that Natsu and Lucy are paired for a school project that involves exploring the magical history of their high school. Along the way, they discover a hidden room in the school that was once used by powerful mages in the past. This leads them on an adventure to unlock the secrets within and also brings them closer together as friends.