Another option could be a new character. A mysterious and powerful ninja from another village who Fem Naruto met during a diplomatic mission. They had a short - lived romance, and he doesn't even know about the child. This would add an element of mystery and the potential for the father to show up later in the story.
One possible plot could be that Fem Naruto has been in hiding with her child to protect it from old enemies. Maybe she was in a relationship during a time of peace but things turned bad. Now she's constantly on the move, training her child in secret ninja skills.
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.
One possibility could be that Percy has been leading a double life. Maybe he had a relationship in the past that he kept hidden, and now the existence of the child is coming to light. The story could explore how he copes with this new reality and how it affects his relationships with his friends and family.
Maybe the child has the power of mind control. Hermione is known for her strong mind and intelligence. Her child could inherit a more extreme version of this, being able to control the minds of others. This could be a very dangerous or useful power depending on how the child is raised and what their intentions are.
The plot might involve the child being hidden away for their safety. Since Naruto and Hinata are well - known and powerful, there could be many who would want to harm the child. So they grow up in a secret location, perhaps with only a few trusted people knowing their true identity. As they grow older, they start to discover their heritage and the responsibilities that come with it.
The child could be very determined like Naruto. They would inherit his never - give - up attitude. For example, when facing difficult challenges in training or battles, they would keep pushing forward no matter what. And also be kind - hearted like Hinata, always showing compassion to others.
Naruto would be a very loving and supportive father. He'd probably be a bit overprotective at times because of all the dangerous things he's faced. But he'd also encourage his child to be independent and follow their dreams. He'd be there to teach them ninja techniques and share his own experiences to help them grow.
Another possibility is Harry Potter himself. This would be a very different take on their relationship. In some fanfiction, the strong bond between Hermione and Harry could be taken to a new level. Maybe in a situation where they are the last hope for the wizarding world, they conceive a child in secret to carry on some special magic or power that could save the wizarding community.
It could be Hinata. In the original series, Hinata has a deep affection for Naruto. In a fanfiction, it would be a natural progression for her to be his secret fiance. Maybe they got engaged secretly to avoid some political unrest in the village.