One idea could be that Fem Luffy, with her Mythical Zoan power, discovers a hidden island full of ancient secrets related to her Zoan form. She has to face challenges there that test her newfound abilities.
A cool plot could be that Fem Luffy's Mythical Zoan ability allows her to enter a different dimension where she meets other beings with similar powers. She has to learn from them to control her power better and then use it to protect her crew and the islands she has come to love. This would involve a lot of character development as she adapts to this new side of herself and the strange new world she discovers.
One interesting plot idea could be that Luffy, in her female form, discovers that her Mythical Zoan powers have a special connection to Law's devil fruit powers. Maybe they accidentally trigger a combined power that creates a unique adventure for them. They could go on a journey to find a way to control this new power while also exploring their growing feelings for each other. For example, during battles, they find that they can combine their abilities in unexpected ways, which helps them defeat stronger enemies and brings them closer together.
Suppose her Mythical Zoan is a dragon. Then she could have scales covering parts of her body, like on her arms and legs. Her teeth might become sharper, and she could have small horns on her head. Her eyes would be more reptilian, with a slitted pupil. And she would be much larger and more muscular in this form, giving her an intimidating presence.
To develop Fem Luffy, emphasize her adaptability. Since she has a Mythical Zoan power, she might have to adapt to new situations more quickly. Maybe she has to learn to control her power in different environments, which can also shape her character. For Law, you can delve into his insecurities. In a relationship with Fem Luffy, he might worry about not being able to protect her fully due to her unpredictable Mythical Zoan powers. This can lead to some character growth as he overcomes these insecurities throughout the story.
Perhaps there could be a plot where a magical artifact is lost and it has the power to change the balance in both universes. Naruto and Fem Luffy both hear about it and start their own quests to find it. But then they realize that working together is the best option. They face many challenges, like different types of enemies and environmental obstacles, as they search for the artifact.
A possible plot is that Fem Luffy accidentally gets involved in one of Smoker's investigations in a new island. She initially seems like a hindrance to him, but as the story progresses, they find out that there is a much larger conspiracy at play that involves both the Marines and some powerful pirate groups. They have to work together to expose the truth, and during this time, a strange friendship starts to form between them.
One idea could be that in this fanfiction, the Fem Naruto, with her fox zoan abilities influenced by Kurama, has to face a new and powerful enemy that is specifically targeting her unique form. She could struggle to control the more wild aspects of the fox zoan while Kurama tries to guide her from within. Another plot could involve Fem Naruto and Kurama having to work together to save the Hidden Leaf from a threat that only their combined power can defeat. For example, a dark sorcerer is stealing the chakra of all the shinobi in the village, and they must find a way to stop it.
Some fanfictions interpret it as having a connection to ancient deities. For example, Luffy's fruit could be related to a sun god, giving him the ability to emit intense heat or bright light. Others might see it as a key to unlocking hidden dimensions within the One Piece world, allowing Luffy to travel to places no one else can reach.
Another plot could involve a common enemy. Maybe a new powerful pirate group attacks both Amazon Lily and Fem Luffy's friends. Hancock and Fem Luffy have to work together to defend. During the battle, Hancock realizes Fem Luffy's strength and leadership skills, and they gradually fall in love as they fight side by side. After the battle, they start to explore their relationship more deeply.
Well, it depends on how the fanfiction is written. In some fanfictions, the author might enhance the powers of Luffy's Mythical Zoan Devil Fruit to make it seem more overpowered. For example, they could give it additional abilities like the power to control certain elements that are not present in the original. However, in the original story, Oda has carefully balanced Luffy's powers. So, it's hard to simply say one is more powerful than the other as they exist in different creative realms.
Maybe they find a strange fruit that has the power to temporarily swap their abilities. This leads to some comical and also interesting situations. Luffy tries to use Robin's powers to reach for things in a more elegant way, and Robin attempts to use Luffy's stretching ability to explore hard - to - reach places. It also makes them understand each other's perspectives better.