In the comics, Barry Allen and Iris have a complex relationship. Sometimes they face challenges and separations, but ultimately, they often find their way back to each other.
The main characters are obviously Barry and Iris, who are the parents. And of course, their baby is a central character as well. There might also be other characters from the Flash universe like Cisco and Caitlin who could play important roles, like helping Barry and Iris take care of the baby or dealing with any threats that come up because of the baby.
There could be a fan fiction where Barry and Iris are on a time - traveling mission. They visit different eras in their past and future, which gives them a deeper understanding of their love and destiny. Along the way, they encounter old friends and foes in unexpected ways.
One common theme is the exploration of their shared history. In many fanfictions, the authors go back to their childhood memories and how those experiences shaped their relationship. Also, the theme of trust is quite prevalent. Since they are in a relationship that has its own set of challenges, showing how they build and maintain trust is a big part of these stories. There's also the theme of hope, that no matter what difficulties they face, they always have hope for their future together.
Well, sometimes in barry and iris baby fanfiction, there are plots where the baby has a unique connection to the Speed Force. Maybe the baby can communicate with other speedsters through the Speed Force in a way that Barry and Iris don't understand at first. It could lead to all kinds of adventures as they try to figure out what this connection means and how to protect the baby from those who might want to exploit it.
To write a good Barry Iris fan fiction, do some research on the show's lore. Know the rules of the Flash's powers, the history of Central City, and the relationships between the characters. This will make your story more believable. Then, just start writing. Let your creativity flow and don't worry too much about making it perfect at first. Edit later to refine your work.