If Jaune and Ruby time travel, Jaune might become more confident in his abilities. Seeing the past and how things could have been done differently, he could learn from his mistakes and grow into a more assertive leader. For Ruby, she might gain a deeper understanding of the history and the weight of her role. This could make her more determined and perhaps a bit more cautious as she realizes the consequences of every action.
Maybe they travel to a time long before the events of the story, during a period when the kingdoms were first being established. They get involved in the ancient politics and power struggles, and in the process, they discover secrets about the origin of the Grimm and the power of the Relics that were long forgotten. Their actions in this past time could have a huge impact on their present world.
Weiss could be one. Since she's Ruby's teammate, she might play a role in the fanfiction. Maybe she's initially skeptical about their relationship but eventually comes to support them. Another could be Blake. She could be involved in helping them out in some situations, like when they face difficulties in their married life. And of course, their mentors like Ozpin or Qrow could also make appearances. Ozpin might offer some wise advice about their relationship, while Qrow could be more of a protective figure, especially towards Ruby.
One idea could be that Ruby and Jaune are partnered for a special mission outside of Beacon. Ruby's speed and combat skills combined with Jaune's strategic thinking could make them a great team. For example, they might be sent to investigate a mysterious Grimm activity in a far - off village. Ruby can quickly scout the area with her speed, while Jaune plans their approach based on the information she gathers.
One possible plotline could be them facing challenges together as a married couple in the world of Remnant. For example, they might have to deal with threats to their new family while also juggling their responsibilities as Huntsmen. Another could be a more comical plot where they struggle to adjust to living with each other's quirks. Maybe Jaune is super messy and Ruby is a neat freak, and they have to find a way to coexist happily.
Her powers might be affected in various ways. If she travels back in time, the Dust and technology available might be different, which could impact how her Crescent Rose functions. Also, the knowledge she has of her powers in the future could either give her an advantage or cause confusion. For instance, if she tries to use a new technique she learned in the future but the conditions in the past don't support it, it could backfire. But on the other hand, she could also discover new aspects of her powers by seeing how they interact with the past environment.
If they time travel, their relationship could become stronger. They'd be relying on each other in a new and strange situation. Having to face the unknown of a different time period would make them depend on one another for support, both emotionally and in terms of survival strategies.
It could be a time - traveling villain who wants to change the past to suit their own evil purposes. Maybe they want to stop Jaune from ever becoming a hero so they can rule the future world unopposed.
Well, they could face a really tough Grimm together. Ruby's Crescent Rose would be slashing away while Jaune uses his shield to protect them both. Maybe Ruby gets injured and Jaune has to step up and use some new combat moves he's been practicing. It would be a moment of growth for him.