The main characters are obviously Sam, Jessica and their baby. Sam and Jessica are the parents, and the baby is the new addition to their family that will likely drive the story forward.
It could also involve the baby having some special ability or characteristic that makes their family's story unique. For example, the baby might be a prodigy in some way, and Sam and Jessica have to navigate how to support and protect their special child.
Obviously, Dean and Sam are main characters. They are the protective older brothers. And then there's the baby sister, who is likely a central figure as well, with her own personality and role in the fanfiction. There might also be other recurring characters from the 'Supernatural' universe like Castiel who could play important parts in the story.
Obviously, Bella and Sam are the main characters. Bella is the one who is pregnant, so she will likely be dealing with a lot of emotions and physical changes throughout the story.
Another possibility is that there is a mysterious figure who has some sort of vendetta against the family. This figure could be causing strange and unexplained events to occur around the baby, like making the baby sick in a way that doctors can't figure out at first. This would then be a source of conflict as Bella and Sam try to protect their baby from this unknown threat.
Vlad could be a great antagonist. He might see the baby versions of Danny and Sam as an opportunity to finally get rid of Danny for good. He could try to use their weakened state to his advantage and steal Danny's powers once and for all.
Another theme is the idea of redemption. Some fanfictions have Jessica coming back in some way, and Sam sees it as a chance to make things right, to protect her better this time. It's like he gets a second chance at their relationship, which ties into the whole redemption concept in the Supernatural world.
Obviously, Loki would be one of the main characters. And of course, his baby. There might also be other characters like Loki's friends or enemies from the original mythology or the related fictional works, such as Thor, Odin, or the Avengers if it's set in a more modern - day superhero - related universe.
In 'sam meets galloway fanfiction', Sam and Galloway are the central figures. Sam could be a young and adventurous soul, ready to take risks. Galloway might be older and wiser, serving as a sort of mentor to Sam as their relationship develops.
Well, clearly Naruto and Jetstream Sam are the main characters. Naruto, a young ninja from the Hidden Leaf Village with his orange jumpsuit and dreams of becoming Hokage. Jetstream Sam, on the other hand, is a skilled swordsman with his own set of unique abilities.
Well, obviously Sam and Tim are the main characters. Sam might be the more impulsive one, always ready to jump into action, while Tim could be the more cautious and strategic thinker.