Their relationship would likely become more serious. They would have to think about not just themselves but also their baby. There would be more commitment and responsibility between them.
You can try searching on fanfiction websites like Fanfiction.net or Archive of Our Own. Just type in 'Gray Juvia pregnant' in the search bar, and you might find some interesting stories.
At first, Gray might be in shock and a bit distant as he tries to come to terms with the pregnancy. But as time goes on, he would start to be more involved. Juvia would be glowing with happiness and that might draw Gray in more. They would start to rely on each other more, sharing responsibilities like doctor visits and preparing for the baby. Their relationship would shift from a one - sided pursuit by Juvia to a more equal partnership, bound by their love for the unborn child.
The plot could involve Juvia and Boras having to adapt to the new situation. Juvia might have to change her lifestyle, and Boras may need to take on more responsibilities. There could also be a sub - plot about the magical or fantastical elements in their world affecting the pregnancy, for example, some magic that could either help or pose a threat to the unborn baby.
One idea could be that they face challenges in preparing for the baby's arrival. Maybe they struggle to find a suitable place to live as a family. Another could be that their friends in the guild throw a big, fun baby shower for them.
Perhaps a plot twist could involve some sort of magic that endangers Juvia's pregnancy. Gray then has to go on a dangerous quest to find a cure or a way to protect Juvia and the unborn child. He might have to face his own inner demons along the way as well, since he has always been a bit of a loner and this new responsibility scares him.
Often, there are plots involving how their friends in Fairy Tail react. They could be really supportive, throwing baby showers and helping with preparations. Another plot could be about Juvia's pregnancy cravings and Gray trying to fulfill them in his own clumsy but endearing way. It's also possible that there are some challenges like Juvia having a difficult pregnancy and Gray being worried sick, but they get through it together with the love and support of their friends.
In a 'Juvia Gets Drunk' fanfiction, Juvia would most likely interact with the members of Fairy Tail. She might start bothering Natsu, asking him silly questions like if he can really breathe fire while drunk. She could also interact with Happy, and they might get into some sort of funny exchange, like Juvia trying to teach Happy a new song she made up in her drunken state. And of course, she'll interact with Cana. Cana being the drinker she is, might find Juvia's drunk behavior either hilarious or relatable and they could have a long chat about different kinds of drinks.
You can try looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a wide variety of fanfics, including ones about Gray and Juvia being pregnant. Just use the search function and type in 'Gray x Juvia pregnant' and you might find some great reads.