Well, in some fanfictions, a plot twist could be that Naruto and Hinata's marriage is part of a grander scheme by an unknown force. Maybe they are unknowingly being manipulated to produce a child with a special power. Another interesting twist could be that Hinata gets transported to an alternate dimension where Naruto doesn't exist, and she has to find a way back to her own world and her husband. And yet another could be that Naruto loses his memories after an accident, and Hinata has to make him fall in love with her all over again while also protecting him from those who might take advantage of his amnesia.
A possible plot twist in Naruto and Hinata married fanfiction is that they find out there is a prophecy related to their union that affects the entire ninja world. Or perhaps, an old enemy resurfaces and targets Hinata because of her connection to Naruto. This forces Naruto to make difficult choices between protecting the village and saving his wife. Also, there could be a situation where Hinata's family disapproves of something Naruto does as Hokage, creating tension in their marriage.
There could be a plot twist where Ayame turns out to be a key figure in an ancient prophecy related to the Hidden Leaf Village. Her marriage to Naruto is part of fulfilling that prophecy, but there are forces that don't want this to happen. So they try to stop the wedding. This could lead to a series of battles and challenges that Naruto and Ayame have to face together, ultimately strengthening their bond in the process.
Well, a plot twist could be that Hinata is actually from a future where something bad has happened, and she came back in time to marry Naruto secretly to change the future. Maybe in the original timeline, Naruto dies or the village is destroyed, and their secret marriage is a key to prevent that. Also, there could be a character who is jealous of their relationship and tries to expose their secret marriage, creating all kinds of chaos and drama.
A great plot twist could be that Sasuke suddenly loses his sharingan and has to rely on his other skills and the help of the others. Naruto might have to train Sasuke all over again, and Hinata and Sakura could be involved in finding a way to restore Sasuke's sharingan. It would change the dynamics of their relationships and how they interact with each other.
In 'The Switch of Fates' fanfiction, Naruto and Hinata's roles are sort of switched. Hinata is the one who has to go on a big adventure to save the village while Naruto is the one supporting her from the sidelines at first. It flips the typical narrative and creates a whole new set of interesting situations and character developments.
One interesting plot twist could be that Hinata loses her memory. Naruto has to work hard to make her fall in love with him all over again. He shows her all the things they used to do together, and slowly, she starts to remember bits and pieces. This adds a whole new layer of drama to their relationship as Naruto is desperate to get back what they had and Hinata is confused yet drawn to him.
One interesting plot twist could be that Naruto initially thought he was only in love with Hinata, but during a dangerous mission where Hanabi's life was on the line, he realized he had deeper feelings for her as well. Another could be that there is a prophecy that foretells of a union between the Uzumaki, Hinata, and Hanabi which would bring great power and peace to the ninja world, forcing the characters to consider this unconventional relationship.
A great plot twist could be that Hinata is actually related to a powerful Soul Reaper family in the Bleach universe. This could be revealed when she starts to show an unusual connection to spiritual energy. Maybe she has an ancestor who was a Soul Reaper and left a hidden power within her bloodline that only activates when she enters the Bleach world.
One interesting plot idea could be a story that focuses on their wedding preparations. It could show how Naruto, who is not used to all the formalities, struggles with choosing the right wedding kimono or learning the proper wedding etiquette. Hinata, on the other hand, is more in tune with the traditional aspects but is nervous about becoming the wife of the Hokage. Another idea could be a time - travel fanfic where they go back in time to their first meetings and relive those moments with the knowledge of their future together. It would be a chance for them to see how far they've come and how their relationship has developed over the years.
One possible plot twist could be that Naruto and Hinata have to quickly learn to control their newfound Jinchuuriki powers. Maybe they are suddenly thrust into a situation where an ancient evil is awakened and only their combined Jinchuuriki abilities can stop it. For example, they might discover that there is a hidden prophecy about two Jinchuuriki working together to save the world.
One possible plot twist could be that Hinata discovers a new power within herself during the fight against Pain. Maybe she can tap into some ancient Hyuga ability that even she didn't know existed. This new power could turn the tide of the battle and surprise both Naruto and Pain.