Maybe Naruto is a secret girl in the sense that he has to disguise as a girl for a mission. And during this time, he discovers a whole new side of the female world in the ninja village. He could learn about the different expectations and challenges that girls face, and this could change his perspective on them.
One idea could be that the Samurai Girl is on a mission in the Ninja world and crosses paths with Naruto. They initially have misunderstandings due to their different cultures but gradually learn to work together. For example, she might be tasked with retrieving a stolen samurai artifact that has ended up in the hands of a rogue ninja. Naruto, being the helpful and curious person he is, decides to join her in the quest.
In this type of fanfiction, a great plot idea could be that Naruto's female identity is tied to some sort of ancient prophecy. Only as a girl can she fulfill this prophecy which could involve saving the ninja world in a different way than in the original story. Her secrecy then becomes crucial not just for her own safety but for the fate of the entire world. And as she tries to keep her secret, she has to navigate the challenges of being a girl in a world that expects her to be a boy.
One plot idea could be a Pokemon girl from the Pokemon world somehow ends up in the Naruto world. She might use her Pokemon to help Naruto and his friends in a battle, like using a water - type Pokemon to put out a fire jutsu - started blaze. Another idea is that a Naruto character travels to the Pokemon world and teams up with a Pokemon girl to participate in a Pokemon tournament there.
Another plot could be that Naruto, as a girl, is underestimated by many in the village at first. But Sasuke sees her potential early on. This leads to a special bond between them where Sasuke becomes her protector and mentor in some ways, and Naruto tries hard to prove herself worthy of his attention and respect. They might go on missions together where Naruto's femininity adds a new dynamic to their teamwork.
One plot idea could be that the dragon girl is from a hidden land and she comes to the Ninja World. Naruto, being curious, befriends her. They could go on adventures together, like finding a powerful ancient scroll that is said to hold the secrets of both their worlds. Another idea is that the dragon girl has a special power that is needed to stop an upcoming evil in the Ninja World, and Naruto helps her harness and control it.
Another scenario could be that Naruto pretends to be a girl to get closer to a reclusive female ninja who only trusts other women. He disguises himself to befriend her and uncover the reason for her isolation. Along the way, he has to keep up the act, which includes having to deal with unwanted male attention that he didn't anticipate.
One plot idea could be that Naruto has a secret training regime away from the village. He discovers a hidden cave where he finds ancient scrolls that teach him unique jutsu not known in the village. This new knowledge makes him even more powerful and he has to keep it a secret as he doesn't know if the jutsu are safe or how the village will react.
One idea could be that a girl uses the henge technique to transform into different characters while at the beach in a swimsuit. For example, she could transform into Naruto to compete in a beach volleyball game in his style, leading to some comical and action - packed moments.
One plot idea could be Naruto, as a girl, using her unique charm and ninja skills to unite the different ninja clans in a more diplomatic way. For example, instead of fighting, she could negotiate treaties through her friendly and approachable nature. Another could be her facing different challenges in the ninja world that are often male - dominated, and breaking gender barriers as she rises to become a respected ninja.
One idea could be that Naruto, as a girl, has to deal with different social expectations in the ninja world. For example, she might face more scrutiny when it comes to combat training, but she uses her unique charm and new perspective to prove herself. Another plot could be that she gets involved in a different kind of relationship with Sasuke. Since she's now a girl, their dynamic might change in unexpected ways, like Sasuke being more protective or Naruto having to break through different barriers in their friendship/relationship.