Yes, there are some. You can find them on various fanfiction websites. Some are really creative, imagining how their different powers would interact in a relationship and how they would rule their combined kingdoms in a unique way.
Common themes include power - sharing and the building of a new kingdom. Given their ice - based powers, they could create a utopia of ice. There's also the theme of family acceptance. How would Elsa's sister Anna react to her marrying Jack Frost? And how would the guardians (if Jack Frost's backstory with the guardians is considered) accept Elsa? These relationship - based themes add depth to the fanfiction. Also, many fanfictions play with the idea of the seasons and how their union might affect the cycle of nature, like creating a perpetual winter that is both beautiful and not harmful to their people.
Well, they would face acceptance issues. The people of Arendelle may be afraid of Jack Frost at first. He is a being associated with cold and winter, which can be seen as a threat. For Elsa, she would have to deal with the fact that Jack is used to a very different lifestyle, constantly on the move in the magical world. And then there are the power struggles. Their combined ice powers could be extremely strong. If they don't learn to control it together, it could lead to problems not just for Arendelle but for other surrounding areas as well. They also need to find a way to balance their personal lives with their new responsibilities as a married couple in two very different worlds.
Love across different realms is also a major theme. Jack Frost comes from a different mythological or magical background compared to Elsa from Arendelle. Their marriage in fanfiction represents the idea that love can transcend these differences. Fanfictions often explore how they bridge the gap between their two worlds, whether it's through sharing their magic or learning about each other's cultures and ways of life. This can involve things like Jack introducing Elsa to the more wild and untamed aspects of winter magic, while Elsa shows Jack the more structured and civilized side of Arendelle.
One popular 'Elsa married Jack Frost' fanfiction might be 'Frozen Hearts United'. It often explores their relationship in a magical world filled with ice and snow. The story could show how they first meet and gradually fall in love, and then their grand wedding which combines the elements of Arendelle and Jack's realm.
One possible plot could be that Elsa, from Arendelle, and Jack Frost, from his own wintry realm, meet by chance during a magical snowstorm that bridges their two worlds. At first, they are curious about each other's powers over ice. As they spend more time together, they start to fall in love. Their relationship might face challenges like how the people of Arendelle would accept Jack, a magical being not from their world. But in the end, they overcome all the obstacles and have a beautiful wedding ceremony with ice sculptures and snowflakes everywhere, uniting their two different worlds in a celebration of love.
One possibility is that it could be a story full of magic and adventure. They could combine their powers to protect their new kingdom. Maybe they'd create ice sculptures together that come to life and serve as their protectors.
Well, it's possible that such a fanfiction exists. Elsa and Jack Frost are from different fictional universes (Elsa from Frozen and Jack Frost from Rise of the Guardians), but in the world of fanfiction, people often cross over characters and create all kinds of scenarios. However, I haven't personally come across a 'pregnant' fanfiction involving them. You might have to search on some dedicated fanfiction websites to find out for sure.
Their wedding could be a magical affair. It might be held in a winter wonderland, with ice sculptures as the decorations. Elsa could walk down an aisle made of ice crystals, and Jack Frost could be waiting at the altar with a big smile. The guests could include all the characters from their respective stories, like Anna, Kristoff, Olaf from Elsa's side, and the Guardians from Jack's side.
One great 'Jack Frost x Elsa married' fanfiction might be 'Frost and Ice Union' which beautifully weaves their two magical worlds together. It shows how Jack's carefree nature compliments Elsa's more reserved self as they embark on a married life in a fictional Arendelle filled with new magical adventures.