There's also the possibility that the mother is a non - ninja. Maybe she was a civilian in Konoha who caught Kakashi's eye. They got involved in a relationship, and she became the mother of his daughter. This would add an interesting dynamic as the daughter would have to navigate between the ninja and civilian worlds.
It could be an original character created just for the fanfiction. Maybe a mysterious ninja woman who crossed paths with Kakashi during a mission and they had a brief but intense relationship.
Perhaps she could be someone from another village. For example, a kunoichi from the Hidden Mist Village who came to Konoha on a diplomatic mission and fell in love with Kakashi. Their relationship was kept a secret at first, and she later gave birth to their daughter.
Well, perhaps the story could be about the daughter discovering her own unique abilities that are different from Kakashi's. This could lead to some interesting father - daughter bonding moments as he tries to help her develop those powers. Also, there could be a plotline where the daughter gets involved in a mission that is related to Kakashi's past, and they have to work together to solve it.
In such fanfiction, the Kakashi OC often has unique physical features. For example, they might have distinct hair color or eye shape that sets them apart.
Maybe an organization that wants to use her unique abilities. If she has inherited some special power from Kakashi or has her own distinct skills, an evil organization could try to capture her and force her to work for them. They would be the main obstacle she has to face in the story.
Perhaps the story focuses on her relationship with the other ninja in the village. She might be friends with the children of Kakashi's old comrades, and they get into all sorts of adventures together, protecting the village from small - scale threats at first and gradually facing bigger challenges.
It could be a new group of rogue ninjas who oppose the ideals of the Hidden Leaf Village. They might target Kakashi's daughter because of her connection to Kakashi and Naruto, seeing her as a symbol of the village's new generation of strength.
Well, it could be about Kakashi's daughter becoming a great ninja like her father. Maybe she trains under Naruto and learns some of his unique jutsu. She could also face challenges in the ninja world, like dealing with powerful enemies or trying to live up to her father's reputation.
The story might be about the OC having a special power. Kakashi is initially intrigued by this power and then falls for the person behind it. Once married, they work together to use the OC's power for the good of the village. They might also have some domestic scenes, like cooking together and having small arguments over silly things that show their normal married life.
Kakashi would likely be shown as a loving and protective husband. He would still be the skilled ninja we know, but he would also have a soft side for his OC spouse. He might share his past traumas with her and let her in on his more vulnerable side.
It could be some rogue ninjas who target Sakura because of her relation to Kakashi. They might think they can use her to get to him or extract information from him.
I think Naruto could be one of the main characters. Since he's Kakashi's student, he might have a special relationship with Kakashi's daughter too. Maybe he acts like an older brother to her.