Perhaps the plot twist is that Naruto has to hide his new vampire nature from his friends in Konoha. This would create a lot of internal conflict for him. He might be afraid that they'll reject him if they find out. And at the same time, he has to deal with the new cravings and instincts that come with being a vampire. It could lead to some really tense and emotional moments when his friends start to suspect something is wrong.
A major plot twist could be that the vampire who bit Naruto is actually part of a larger conspiracy against the ninja world. Naruto, now with his new vampire powers, is the key to either stopping or starting this conspiracy. He might find out that the vampire's bite was not an accident but a carefully planned move to use him as a weapon or a sacrifice. This would force Naruto to make some difficult choices about who to trust and what to do with his new powers.
It could be that the bite was part of a larger plan by Orochimaru to create a new body for himself. Orochimaru is always seeking new vessels. He might think that Naruto, with his strong chakra and willpower, would be the perfect host. So, Naruto has to fight against Orochimaru's influence from within his own body, while also trying to figure out how to stop Orochimaru's overall plan.
The consequences could be far - reaching. Naruto's relationships would surely be strained. His relationship with Sakura, for instance, might become complicated as she may be afraid of him or try to find a way to cure him. His bond with Sasuke could also be tested. Sasuke, being more attuned to darker powers, might have a different reaction compared to others. Moreover, Naruto would have to deal with the vampire community if there is one in the fanfiction world. He would need to learn their rules and how to control his new urges, or else he could become a danger to those he loves.
Maybe Naruto finds out that there are some English magic users who mistake him for a powerful wizard due to his chakra abilities. This misunderstanding could create some really interesting and comical situations, like when they try to enroll him in their magic school and he has to explain his ninja powers.
A possible plot twist is that when Harry is bitten, he starts to have visions of the vampire's past. This leads him to discover a long - forgotten prophecy about a vampire - wizard hybrid saving the wizarding world. Also, his friends initially think he's turned evil due to the vampire bite, but in reality, he's just trying to figure out how to use his new state to fight the real threats in the wizarding world. It could also be that the bite makes Harry age backwards, which causes all sorts of chaos in the wizarding world as people don't recognize him and he has to re - establish his identity.
Perhaps a plot twist is that when Hermione is bitten, she gains a special connection to the werewolf pack. Instead of being an outcast, she becomes a sort of mediator between the wizarding world and the werewolves. This causes a stir in both communities as they have to re - evaluate their views on werewolves and those bitten by them.
In this fanfiction, after Stiles gets bitten by a vampire, he might find himself in the middle of a vampire war. The vampire who bit him could belong to one faction, and now the other faction sees Stiles as a threat or a tool. He has to learn about vampire politics and hierarchies quickly. His friends, especially those who know about the supernatural, would try to protect him. Stiles would also have to deal with the physical and emotional changes that come with being a vampire, like the isolation that can come from living a nocturnal life and the fear of hurting those he loves.
One possible plot twist could be that Naruto's unorthodox training methods clash with the more traditional approach of Team 10. For example, Naruto might try to introduce his shadow clone training, but the members of Team 10, like Shikamaru who prefers more strategic and less energy - consuming methods, initially resist. This could lead to some interesting character development as they learn from each other. Another plot twist could be Naruto's relationship with Ino. Since Naruto has a history with Sakura, Ino might be jealous or feel threatened at first. But as they work together on missions, they could develop a unique bond, perhaps even a friendly rivalry that helps both of them grow stronger.
A plot twist could be related to Yugito's tailed beast. Maybe the power of the two - Naruto's Nine - Tails and Yugito's Two - Tails - has some unforeseen consequences when they get married. It could attract the wrong kind of attention from those who seek to use tailed - beast power for evil. Or perhaps the tailed beasts themselves have some sort of reaction to their union that changes the relationship between Naruto and Yugito, like they start to communicate with each other in a new and strange way through the beasts.
One possible plot twist could be that Tsunade trains Naruto not just in physical combat like she did with others, but also in medical ninjutsu. This would be unexpected as Naruto is more known for his brute force. Maybe Naruto uses his new medical skills in a creative way during a battle, like healing his opponents to show mercy and then defeating them when they are off - guard.
Another plot twist could be that Naruto getting the Sharingan is part of a much larger conspiracy. The Akatsuki might be behind it, trying to create a super - powerful being that they can control. So Naruto has to figure out who's behind this while also dealing with the new power. He might find that there are some hidden motives among his own allies as well, which would really shake up the story.