In many fanfictions, Sakura could be a potential mother. Since she has a close relationship with Naruto in the original series, some fans might imagine a scenario where they end up together and have a son. Another possibility could be Hinata. Given her deep love for Naruto, it's not hard to fathom a fanfiction where they have a secret son.
Well, it could be an original character as the mother in the fanfiction. Writers often create new characters to add unique twists to the story. Maybe this new character has a special connection with Naruto that led to the birth of their son. It gives more creative freedom to the author to build a whole new plot around this new relationship.
It could be Hinata. Even though in the original story they are openly married, in a fanfic scenario, there could be a situation where their relationship was kept secret for some time and she gave birth to a son secretly. Maybe due to some threat to the village or Naruto's safety.
It could be a random villager that Naruto met during one of his travels. Maybe she was from a small village that Naruto helped protect, and they had a brief encounter that led to the child.
There's also the possibility that it could be an original character created just for the fanfiction. This would give the writer more creative freedom to shape the story around the relationship between Batman and the mother, and how it impacts their son.
It could be an original character created just for this fanfiction. Maybe a girl who Stiles met during a summer vacation and had a brief fling with.
It could be Ginny. Even though in the original story they are married and have kids in a more normal way, in fanfiction, there could be a twist where their relationship had a secret earlier on and she is the mother of the secret child.
It could be an old acquaintance that Percy had a brief relationship with. Maybe someone he met during one of his adventures and then lost touch with, but she later discovers she's pregnant and decides to keep the child a secret from Percy for various reasons.
The mother could also be a completely new character created specifically for this fanfiction. She might be from a different realm or have some special powers. And her relationship with Percy could be a complex one, filled with secrets and misunderstandings that led to the situation of having a secret daughter.
Annabeth could be the mother. Since she and Percy have a strong relationship, it would be a natural choice. Their son would inherit both their intelligence and combat skills.
In some fanfictions, the mother could be an original character created by the author. This allows for a lot of creative freedom in developing the backstory and relationship dynamics.
It could be Hinata. Since they got married in the original series, it would be a natural choice. Their son would inherit Hinata's gentle nature along with Naruto's determination.