Maybe it's an adopted child. Naruto, with his big heart, could have taken in an orphan from one of the village's tragedies. This would give him the role of a single mother in a very unique way as he tries to instill his values and ninja skills in the child.
It could also be a new character entirely. A child that the author of the fanfiction creates specifically for this story. This would allow for a completely fresh take on Naruto's role as a single mother, as he navigates the challenges of raising a child with no pre - existing storylines to follow.
It could be a completely new character created just for this fanfiction. Maybe a child with some unique abilities that Naruto discovers and decides to take under his wing.
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.
Another possibility is that the father could be a completely new character created just for the fanfiction. This new character could be a mysterious wizard who had a short - lived encounter with Hermione and then disappeared, leaving her to deal with the pregnancy on her own.
In a fanfiction like this, it could start with the single mother being a refugee from another village. Naruto, in his quest to bring peace and unity, offers her shelter in Konoha. Her child is initially scared in the new environment, but Naruto helps them adjust. Through these interactions, the single mother sees Naruto's true character. They start to bond over shared experiences of loneliness (she as a single mother, Naruto having grown up without his parents for a long time). Eventually, love blossoms and they get married.
It could be a child of one of Naruto's friends who passed away. For example, if Shikamaru died in a battle, Naruto might take in his child. Naruto would then try to pass on Shikamaru's wisdom and strategic thinking to the child, along with his own ninja skills.
Maybe it could be a new character. A mysterious woman who Percy meets during one of his adventures. This would add an element of mystery to the story.
In some fanfictions, Naruto's mother might be a character related to the Uchiha clan in a unique way. It could be someone who was secretly in love with an Uchiha and had Naruto as a result. Maybe she was a long - lost relative of the Uchiha who was trying to protect the clan's secrets through Naruto.
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.
It could be an orphan who has been living on the streets of the Hidden Leaf village. This child might have some hidden potential, like being a descendant of a powerful ninja clan but unaware of their heritage.