Well, perhaps Killian could be a stranger who stumbles upon baby Emma. He might be instantly charmed by her innocence. Maybe he has some sort of premonition that she will grow up to be an important person in his life. He could then decide to protect her from any harm in the area, starting a connection that would later develop into a more complex relationship as Emma grows up.
In the fanfiction, Killian might be a sailor docking at a port town. There, he hears the cries of baby Emma. He goes to check it out and finds her in a rather poor situation. He decides to use his resources (maybe some money he got from his latest voyage) to ensure she is well - cared - for. This act of kindness starts a chain of events that ties their fates together. As he continues his adventures, he always has a thought in the back of his mind about the little girl he once helped.
One possible plot could be that Killian is sent to find teen Emma by some magical force. He finds her and at first, she is very distrustful of him. But as time passes, they start to understand each other. Killian tells her stories about her future self (without giving away too much) and helps her gain confidence. This fanfiction could explore their relationship in a new light, different from their relationship when she is an adult. It could also show how Killian's presence in teen Emma's life could shape her into the person she becomes as an adult in the show.
In the fanfiction, it might be that Killian is magically bound to help child Emma find something important, like a lost family heirloom or a key to a magical place. As they journey together, they form an unlikely bond. Killian teaches her some skills, and Emma, in her innocent and curious way, makes Killian see things from a different perspective. Their interactions could be filled with humor, as well as moments of emotional growth for both characters.
In this fanfiction, the plot might revolve around the idea that Killian and Emma are in a world full of magic and danger. When they learn they're having a baby, they have to be extra careful. They might seek the help of their magical friends to ensure the baby's safety during the pregnancy. As the due date approaches, they face a final battle against an evil force that wants to harm their unborn child, and they triumph just in time for the baby to be born healthy.
Obviously, Killian and baby Emma are the main characters. Killian could be a character with a mysterious past, and his encounter with baby Emma might be a turning point in his life. Baby Emma, being so young, represents potential and new beginnings. The story might focus on how Killian's actions towards the baby shape both their futures, and we could expect other secondary characters to interact with them as the story progresses.
Another common theme is growth. Both Emma and Killian grow as individuals and as a couple. Parenthood forces them to face new challenges and they develop new skills and understanding. For example, Killian might become more patient and Emma more nurturing.
One common theme is the discovery of a new connection. Killian and young Emma are from different backgrounds, and when they meet, they start to find things in common or are intrigued by each other's differences.
Love is also a big theme. The love between Emma and Killian grows deeper with the presence of their baby girl. And of course, their love for their daughter is central. There are often sweet moments of them expressing their love for the baby. For instance, Killian whispering words of love to the baby girl while she sleeps. Another theme is growth. Both Emma and Killian grow as individuals as they take on the responsibilities of parenthood. They learn new things about themselves and each other. This is often shown through their interactions with the baby girl, like when Emma realizes she can be more patient because of her daughter.
One interesting Killian and Emma baby fanfiction could be about their journey of becoming parents. It might show how they adjust their lives to take care of the baby, like Killian learning to change diapers and Emma dealing with sleepless nights. The story could also involve their friends in Storybrooke helping them out and giving advice on parenting.
One idea could be that Killian is on a quest and stumbles upon a young Emma in a magical forest. He initially mistakes her for someone else but soon realizes her potential. Another could be a time - travel scenario where Killian goes back in time and meets a young Emma, and he has to protect her from a dark force without changing the future too much. And perhaps a story where young Emma is lost in a different realm and Killian is the one who finds her and they form an unlikely bond.
Killian could develop from a more carefree adventurer to a responsible and protective father. He might learn to be more patient and less impulsive as he anticipates the arrival of his baby.