Perhaps Idun's pregnancy is a result of some magical event, and the Snow Queen, out of jealousy or a desire for power, tries to either harm Idun or use the unborn child for her own purposes. It could also be that the Snow Queen has a change of heart and decides to protect Idun and the baby, leading to a story of redemption.
I'm not aware of specific fanfiction on this exact topic. You could try searching on fanfiction platforms like Archive of Our Own or FanFiction.net.
One possible theme could be the journey of the character during pregnancy, like dealing with new emotions and changes. For example, in a Frozen - inspired story, it might explore how the character adjusts to the physical and emotional aspects of pregnancy while also being in the magical world of Frozen.
One possible plotline could be that Elsa discovers she's pregnant and has to deal with the newfound powers that might be affected by her pregnancy. For example, her ice powers could become more unpredictable. Another could be Anna's pregnancy journey, where she has to balance her duties in Arendelle with the anticipation of motherhood. She might worry about how to raise a child in a kingdom that has faced so many challenges.
I'm not sure specifically about 'frozen idun pregnant belly' fanfiction. You could try searching on fanfiction - specific websites like Archive of Our Own. They might have some related works if they are within the site's guidelines.
Well, a plot could involve Elsa feeling lost and out of place in her own world. She then stumbles upon Idun by accident. Idun, being the goddess of youth and rejuvenation, sees potential in Elsa's powers. They start to exchange knowledge about their respective powers. As they do so, they notice that there are dark forces that are envious of their combined might and try to separate them. So, they must fight to stay together and protect their new - found bond.
One possible plotline could be that Snow White becomes pregnant before she meets the prince. This could lead to her having to hide from the evil queen not only for her own safety but also for the safety of her unborn child. Another could be that after she marries the prince, she faces some sort of magical threat to her pregnancy. Maybe an old enemy of the kingdom tries to harm the heir. Or perhaps she discovers some special power within herself related to her pregnancy that she has to learn to control.
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 that the characters from Frozen enter a time - traveling adventure and witness different versions of their future. For example, Elsa might see a future where she has fully mastered her powers and is using them to create a utopia. Anna could see herself as a great leader, making important decisions for Arendelle. And Kristoff might see his future with Anna and their family.
One possible plotline could be about the challenges Reshiram faces during pregnancy. For example, how it adjusts to its changing body and powers. Another could be the reactions of other Pokémon characters in the story, whether they are supportive or not.
One possible plotline could be the challenges she faces during her pregnancy. Maybe she has to deal with the reactions of her friends and family within the fandom's world. Another could be how she manages her normal duties or adventures while being pregnant.