It might start with a chance encounter. They see each other in a new light and gradually start to develop feelings. Their relationship develops as they exchange kind words and small gestures of kindness.
Their relationship would likely become more solid. Having a baby together means they have a new shared responsibility. They would have to rely on each other more, like when taking care of the baby at night or making important decisions about the baby's future.
At first, they might develop their relationship through helping each other. Hans could assist Elsa in learning about diplomatic relations with other kingdoms, while Elsa could teach Hans about controlling his temper (assuming he has improved). As they spend time together in these educational and growth - oriented activities, they begin to see each other in a new light. They find themselves attracted to the new, improved versions of each other and so they get married.
One possible plot could be that Elsa and Hans meet secretly. They start to share their true feelings and dreams away from the prying eyes of the kingdom. As they fall deeper in love, they face the challenge of how to make their relationship acceptable to the people who have misjudged Hans in the past.
In Elsa and Hans love fanfiction, often there is a lot of character development. Since their initial relationship in the movie was so rocky, the fanfictions usually focus on how they overcome those initial negative impressions. For example, Hans might be written as having a change of heart more thoroughly and Elsa learning to trust again.
It would become more committed. They'd have to work together to take care of the baby. Hans might become more protective, and Elsa would be more nurturing. Their focus would shift from their own issues to the well - being of their child.
Anna would be a likely candidate to rescue Elsa. She loves her sister deeply and has shown great courage in the past. She would stop at nothing to find and free Elsa from Hans.
Anna could be the one to save Elsa. After all, she has proven herself brave and determined in the original story. She would stop at nothing to rescue her sister from Hans's clutches.
After the wedding, their relationship might start off rocky. Elsa would still be cautious about fully trusting Hans after his previous actions. Hans, on the other hand, would have to work hard to prove his loyalty. They might face challenges like dealing with the opinions of the people of Arendelle who are skeptical of their union. But over time, as they communicate more and face difficulties together, they could gradually grow closer.
The idea of an Elsa and Hans love story is a false one. In the Frozen universe, Elsa is a complex character dealing with her own insecurities and the power she has. Hans is a conniving man who wants to take over Arendelle. He fools Anna into thinking he loves her, but there's no relationship with Elsa. Elsa is more concerned with her family and her place in the world, and any thought of a relationship with Hans is completely out of the question as his true nature is revealed to be quite malicious.
One common theme is redemption. Since Hans was initially the villain, a lot of fanfictions focus on him redeeming himself in Elsa's eyes and winning her love. Another theme is the power of love to change people. For example, Elsa, who was so closed off, might open up because of her love for Hans.