Since it's a fanfiction, it could be really diverse in its plot. It may center around Hinata's family history in the past and how that affects her in the Naruto story. Maybe she discovers something about her clan's past that gives her new powers or a new understanding of her place in the ninja world. It could also involve her going back in time to prevent some sort of disaster that was hinted at in the original Naruto series.
Based on the title, Hinata is surely one of the main characters. And since it's related to Naruto, Naruto himself is likely to be an important character as well. There could also be other characters from the Naruto universe, like characters from Hinata's clan such as her father or sister, who might play significant roles in the story as it involves Hinata's journey to the past.
Well, if Naruto and Hinata go to the past in fanfiction, it could be really interesting. They could meet their younger selves. Naruto might see his lonely childhood self and try to give him some hope. Hinata could also see her shy younger self and perhaps encourage her to be more confident earlier. And they could also influence the relationships between other characters. For instance, they might help their friends' parents get together or something like that.
They might try to change some past events. For example, Naruto could prevent some of the early tragedies in the village. Hinata might also get the chance to be more assertive earlier in her life, since she has Naruto by her side this time. They could also have an impact on the relationships between different ninja clans.
In some Naruto fanfictions, Hinata could potentially be portrayed as a 'weapon' in a very metaphorical sense. For example, her Byakugan abilities might be exploited in unique ways that make her seem like a strategic weapon for a side or a cause. But in the canon Naruto story, she is a character with her own agency and not really a weapon.
One great source for Naruto and Hinata fanfiction could be FanFiction.net. You can search for stories specifically focused on their relationship there. There are often new and interesting takes on their story, from how they first fell in love to their married life in the future.
Perhaps in the fanfiction, Hinata wears a micro bikini for a special festival in the Hidden Leaf Village. Naruto is really excited to see her in it. They participate in the festival games together and Hinata's new look makes Naruto see her in a different light, more as a strong and confident woman.
One possible plotline could be a story where Naruto has to choose between two versions of Hinata, the original Hinata and a version from an alternate RTN (Road to Ninja) universe. Maybe in this fanfiction, the different Hinatas have unique abilities or personalities that make Naruto's choice more difficult.
Well, their relationship would likely become more confident. Since they are already married, Hinata wouldn't be as shy around Naruto as she was in the original timeline. Naruto would also be more aware of Hinata's feelings and his own for her. He would probably be more protective of her right from the start.