A possible plotline could be that Jack Frost is on a mission in Rapunzel's world and accidentally stumbles upon her tower. They form an instant connection. As their relationship progresses, Rapunzel gets pregnant. Now, they need to figure out how to raise the child. Jack Frost wants to introduce the child to his icy world, but Rapunzel is worried about the cold environment. Meanwhile, there could be a villain, like an evil witch or a jealous magical being, who wants to harm Rapunzel and the baby. So they have to rely on their combined powers and the help of their friends from both their worlds to protect their family - to - be.
Perhaps the pregnancy is a symbol of a new era of peace between the world of Frozen and Jack Frost's domain. Elsa and Jack Frost have to work together to prepare for the arrival of the baby. They might build a new place that combines the ice and snow elements of both their worlds, and in the process, they face challenges from those who oppose the union, but they overcome them through their combined powers and the power of friendship.
One possible plotline could be her journey in a magical world filled with other mythical creatures. As a female Jack Frost who is also a Pooka, she might struggle to fit in or find her place among the different magical beings.
One possible plotline could be the challenges they face in their relationship due to the unexpected pregnancy. Maybe they have to deal with the reactions of their friends and family.
It's not that common. In the fanfiction world, there are many popular pairings within their own respective story realms. But when you cross Jack Frost and Rapunzel, it's quite out of the ordinary. Writers who create such fanfictions are usually looking to break boundaries and create something that stands out. The pregnancy aspect adds another layer of uniqueness as it delves into a new phase of a relationship that is not typically associated with these characters.
One interesting fanfiction could be where Jack Frost accidentally freezes Rapunzel's long hair and then has to find a way to thaw it without causing her harm. Another might be a story where they meet in a magical forest during a solstice event and team up to defeat an evil sorcerer who is threatening both their worlds.
One possible plotline could be that Hiccup and Jack Frost meet when a strange magical event causes their worlds to collide. They then have to work together to find a way to separate the worlds again while also dealing with the local problems in each other's worlds, like Hiccup helping Jack with some mischievous spirits in Jack's world.
One possible plotline could be that Jack Frost discovers something strange related to Pitch, like a 'lemon' - themed object that has some sort of power over Pitch. And he has to figure out how to use it to either defeat Pitch or make him change his ways.
A common theme is the anticipation and excitement of new life. Both Jack and Rapunzel are likely to be shown as being very eager for the baby to arrive. Another theme could be the challenges they face together as a couple during the pregnancy, like dealing with morning sickness for Rapunzel and Jack trying to be as supportive as possible.
Another theme could be the exploration of the impossible becoming possible in the realm of fanfiction. It would likely be a very creative take on the characters of Jack Frost and Hiccup, with the added element of pregnancy bringing in elements of family, responsibility, and new beginnings in a completely out - of - the - ordinary way. Since this is such an unusual concept, the writer would have a lot of room to play with different themes and ideas.
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.