Well, one possible plot could be that they have to face a lot of challenges together. Since Arya is a strong - willed character, she might struggle with the idea of being pregnant at first, especially in a world as dangerous as 'Game of Thrones'. Jaqen, on the other hand, could be protective. They might have to hide from their enemies who would see a pregnant Arya as a weakness or a valuable target. Another aspect could be how they plan for the future of the child in a world full of chaos and power struggles.
I haven't come across a fanfiction with that exact plot. Fanfiction often explores different relationships and storylines in the 'Game of Thrones' universe. While Arya and Jaqen have an interesting relationship, pregnancy isn't a typical aspect explored in mainstream fanfictions about them. It could be that it exists in some more niche or less well - known works, but it's not something I've seen frequently.
Perhaps in the fanfiction, Arya and Jaqen form an unexpected bond due to the pregnancy. Jaqen, who is usually a mysterious and somewhat aloof character, could show a more caring and protective side. They might have to find a safe place to stay, away from the chaos of their normal lives, and figure out how to raise a child in a world full of danger and intrigue.
Another plot could be centered around Jaqen teaching Arya some of his unique skills. Arya is already a skilled assassin, but Jaqen has his own brand of magic - like his ability to change his face. He could pass on some of this knowledge to Arya, and they could use it to infiltrate enemy strongholds and carry out their plans.
Arya may become more confident in her abilities with Jaqen's guidance. She could grow from a somewhat reckless girl into a more calculated and strategic assassin. For example, she might learn to better plan her attacks instead of acting on impulse all the time.
At first, it could be a teacher - student relationship, with Jaqen teaching Arya more advanced skills of the Faceless Men. As time goes on, they might become comrades, relying on each other in dangerous situations.
One possible plot could be that they are on the run and trying to keep the pregnancy a secret from their enemies. They have to find a safe place to have the baby.
I'm not sure if there's a specific fanfiction where Arya is pregnant. Fanfiction is a vast world with different interpretations. Some fanfic authors might be interested in exploring this kind of relationship development and the implications of Arya being pregnant, but it might also deviate from the original tone and themes of the 'Eragon' series. You could start by looking at fanfiction archives dedicated to 'Eragon' and use relevant search terms.
Perhaps Arya discovers she's pregnant while on a journey with Jaquen. They then have to make decisions about their future. Do they continue their nomadic lifestyle? Or do they find a place to settle down? And there could be internal conflicts within Arya, as she's always been a fighter and now has to embrace a new role as a mother - to - be.
A potential plot might involve Arya and Eragon having to hide their pregnancies at first. Since they are important figures in their world, their pregnancies could cause political unrest or draw unwanted attention from those with ill intentions. As they progress through their pregnancies, they could also discover new magical aspects related to the unborn children, like special powers or a connection to an ancient prophecy. They would then have to deal with the implications of these discoveries while preparing for parenthood.
In some fanfictions, there might be a plot where Jaqen actually has a deeper connection to Arya's family than she initially realizes. Maybe he was secretly tasked with protecting her all along. This could lead to a series of revelations and a change in their relationship dynamics, from mentor - student to something more like comrades in a grander scheme.