Well, in this kind of fanfiction, a really interesting plot twist could be a time - travel element. Imagine Fem Naruto and Neji are sent back in time to before they even knew each other. They have to find a way to get back to their own time while also not changing the past too much. Another plot twist could be that a strange illness affects only ninja who are married to each other, and they have to find a cure together. Or there could be a situation where a powerful artifact is found that has the power to break their marriage bond if misused, and they have to protect it from falling into the wrong hands.
Well, in a fanfiction where Fem Naruto and Neji are married, their relationship could be full of mutual respect. Neji, with his calm and composed nature, might balance out Fem Naruto's more impulsive side. They could support each other in their ninja duties. For example, Neji could use his Byakugan to gather intelligence while Fem Naruto uses her strength and determination in combat. And at home, they might have a warm and loving environment, sharing stories of their day and training together to keep their skills sharp.
One possible plot twist could be that Neji has to go on a dangerous mission right before the wedding. It would put their relationship to the test as Tenten would be worried sick about him. Another twist could be that there's a misunderstanding within their families regarding some old traditions that might affect the marriage. For example, an old family feud resurfaces that threatens to stop the wedding. And a third plot twist could be that Neji loses his memory due to a jutsu gone wrong just days before the wedding, and Tenten has to make him fall in love with her all over again.
One possible plot twist could be that their union causes a rift in the ninja world. Some might oppose it due to Itachi's past actions. Another could be that Fem Naruto discovers a hidden power within herself as a result of their marriage bond. It could also be that an old enemy resurfaces to target them because of their combined strength and the new hope their union represents for the future of the ninja villages.
One possible plot twist could be that their relationship is initially opposed by the village elders. They might see it as unconventional or worry about how it could affect Naruto's role as a potential Hokage. Another twist could be that an old enemy resurfaces and targets Kakashi to get to Naruto, seeing their marriage as a weakness to exploit.
The plot could involve them starting a family. Fem Sasuke might be hesitant at first, worried about passing on her troubled family history. However, Naruto is excited and encourages her. They could have a child who has a unique combination of their powers. And then they have to protect this child from various threats, both from outside the village like rogue ninjas who might want to kidnap the child for its power, and from within the village where some might be jealous or fearful of the child's potential. This would bring them closer together as they work as a team to keep their family safe.
One interesting plot twist could be that Neji discovers a new power within his Byakugan that makes him evenly matched with Naruto's Nine - Tails power. Maybe he unlocks a hidden ability that allows him to see through Naruto's chakra cloaks or disrupt the Nine - Tails' chakra flow. Another plot twist could be that Naruto loses his access to the Nine - Tails' chakra during the fight, and has to rely solely on his own skills and training, making it a much more even match against Neji.
A great plot twist could be that Neji, who was thought to be a loyal Leaf Village ninja, is actually a spy for an enemy village. This would completely change the dynamics between him, Naruto and Sasuke. They would have to figure out how to deal with this betrayal while also dealing with other threats to the village.
One possible plot twist could be that the fem Kyuubi, instead of being an enemy, turns out to be an ally of Naruto the mercenary. Maybe she has her own motives for working with him, like she wants to use his skills to gain freedom from some other powerful force that has been controlling her.
One possible plot twist could be that Naruto's mental instability causes him to misinterpret the Fem Kyuubi's intentions. Maybe he sees her as a threat when she's actually trying to help him. This could lead to a lot of internal conflict within Naruto and also create tension in their relationship.
A plot twist could be that fem Tsukune is actually a long - lost relative of a powerful Naruto character. Maybe she has some special bloodline that links her to someone in the Naruto universe, and this discovery changes the whole dynamic of the story.