The baby could be a lost elf child from a different part of the forest. Maybe their family was attacked by some dark force and Thranduil finds them by chance.
The baby could be a half - demon, related to some other important character in the series. Maybe it's the offspring of a character Sesshomaru has some history with.
One common theme is the power dynamic. Ozai is a powerful figure in the Fire Nation, and how he wields that power over his baby son, Zuko, is often explored. For example, in many fanfictions, he starts to instill in Zuko the importance of strength and power from a very early age.
In the fanfiction, the baby might have a unique appearance. It could have Katara's blue eyes and Zuko's dark hair. Personality - wise, it could be a blend of their traits. Zuko's determination and Katara's compassion. Maybe the baby is also very empathetic, able to sense the emotions of others around it, which is a trait that could come from both of their sensitive natures.
One interesting zuko and katara baby fanfiction could be about their journey of raising a child in a world that is still recovering from war. The story might focus on how they teach their child about the different cultures that they come from.
Love and family would be a major theme. Zuko and Mai's love for each other is shown through their joint responsibility of raising their child. Another theme could be growth. They both grow as individuals as they learn to be parents.
Perhaps the fanfiction delves into the baby's unique abilities or characteristics. Since Zuko has a connection to the Fire Nation and Mai is a skilled fighter, the baby could inherit some extraordinary powers. It could show how they train the baby to control these powers while also giving it a normal childhood.
I'm not sure specifically as I haven't read that particular 'lucy finds a baby fanfiction'. It could be about a character named Lucy who discovers a baby in a story that is fan - created. Maybe it's in a fictional world where she stumbles upon an unexpected baby and then various adventures or emotions unfold from there.
He would be super excited. Zuko would probably be right there on the floor with Izumi, coaxing her to take those first steps. He might hold out a small, shiny object from the Fire Nation as an incentive.
Their relationship would likely become more intimate and complex. They would have to rely on each other more, sharing a bond that goes beyond their previous friendship or alliance. Zuko would probably become more protective of Katara, and Katara would trust Zuko with her vulnerability during pregnancy.