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 really interesting plot twist could be that Naruto and Hinata's secret marriage is part of a larger plan by an ancient prophecy. There is a hidden power or knowledge that can only be accessed through their union. However, there are forces at work that don't want this to happen, so they have to keep it a secret. Their friends start to suspect something is different about them, like Naruto is more protective of Hinata and Hinata seems to know Naruto's thoughts without him saying anything. This leads to some really fun and mysterious moments in the fanfiction.
In fanfiction, it could be for safety reasons. There might be threats or political situations in the village that make them keep their marriage a secret. For example, there could be some groups who oppose their union, and by keeping it secret, they can avoid any potential problems until they are strong enough to face them. Also, they might just want to have a simple, intimate bond without all the formalities and public attention that a normal wedding would bring.
Another plot twist might be that the wizarding world somehow discovers their secret marriage against their will. This could lead to a whole bunch of political and social implications. For example, there could be those who oppose the union due to Hermione's Muggle - born status and Harry being a symbol of the wizarding world. It could spark a movement for or against inter - status marriages in the wizarding community.
Well, a plot twist might be that they got secretly married because they made a drunken bet. One night, after a wild celebration at the guild, they made a bet that if Natsu could complete a really difficult mission on his own within a week, Lucy would marry him. Natsu, being overconfident, accepted. He completed the mission, and Lucy, being a person of her word, went through with the marriage in secret, not knowing how to break the news to their friends and guild mates.
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.
A possible plot twist could be that it was all a ruse. Maybe they faked their marriage for some greater good, like to expose a dark wizard who was targeting married wizards. Another could be that one of them was under a spell and didn't really mean to get married secretly, and when the spell is broken, they have to figure out what to do.
A possible plot twist is that Naruto is actually a reincarnation of a great Jedi. He starts having strange dreams and visions of a past life as a Jedi, and these memories gradually influence his actions as a ninja. His friends might be confused or even a bit scared at first, but as he learns to control this new side of himself, they come to accept and rely on his Jedi - inspired skills in their battles against stronger foes.
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.
A possible plot twist is that Hermione is actually on a secret mission for the Order of the Phoenix when she marries Draco. She's using the marriage as a cover to get closer to some dark wizards Draco has connections with. As they spend more time together in their 'fake' marriage, they start to truly fall for each other, which complicates things for Hermione's mission.
One possible plot twist could be that they keep their marriage a secret from the wizarding world because of the age difference between them. Hermione is much younger than Remus, and the wizarding society might not accept their union easily. Another twist could be that they got married secretly to protect each other. Maybe there's a dark force threatening them, and by being married secretly, they can use some magic spells or charms that are only available to married couples to keep each other safe.
Well, a plot twist could be that while Naruto is saving Hinata and Hanabi, he discovers a hidden power within Hinata that she didn't even know she had. Maybe it gets activated during the rescue and she actually helps Naruto in a way he didn't anticipate. And as for Hanabi, she could be the key to finding a secret passage or something that aids in their escape from the dangerous situation.