Power. Most fanfictions focus on the extreme power of Madara's Rinnegan. They explore how it can be used to dominate battles or change the Naruto world. Another common theme is mystery. Since the Rinnegan has many unexplored aspects in the original series, fanfictions often try to uncover its secrets.
One common theme is power exploration. Writers often delve into how Madara's Rinnegan powers could be used in different scenarios, like battles against other powerful foes. Another theme is redemption. Some fanfictions might explore if Madara could be redeemed with his newfound power. And of course, there are also stories about his past and how he obtained the Rinnegan in the first place.
In some fanfictions, it could be through a strange and powerful jutsu transfer. Maybe Madara, on the verge of defeat, decides to transfer his Rinnegan power to Naruto for some unforeseen reason, like seeing a new path for the ninja world in Naruto.
Naruto would probably win. He has an indomitable will and has always found ways to overcome powerful foes. His experience and the unique powers he might gain with the Rinnegan could give him an edge over Madara.
He could combine the Rinnegan's ability to control gravity with his Rasengan, creating a super - powerful and hard - to - dodge attack.
One common theme is power and its consequences. When a female Naruto has the Rinnegan, she has to deal with the great power it brings. For example, she might face envy from other ninjas or the temptation to use it for wrong reasons.
A frequent theme is adaptation. When the Rinnegan is introduced into a crossover, characters have to adapt to this new power dynamic. For example, in a Naruto - Harry Potter crossover, the wizarding world has to adapt to the existence of the Rinnegan. Also, redemption can be a theme. A character who has misused the Rinnegan may seek redemption in the crossover story.
Love and relationships are also common themes. It could be her relationship with other main characters in Naruto. Maybe she has a romantic interest in a character like Naruto or Sasuke, which creates a whole new dynamic in the story. Or it could be about her friendships or rivalries within the ninja world.
A common theme is the transfer of power and knowledge. Madara Sensei is often depicted as having a vast amount of knowledge about ninjutsu and the ninja world in general. So, in many fanfictions, he passes this on to Naruto.
The theme of redemption can also be present. Madara was considered a villain, but Naruto might see some good in his initial intentions. So, Naruto could try to redeem Madara's name or ideals in a way. He could take the positive aspects of Madara's vision for the ninja world, like unity among the clans, and work towards achieving it in a more peaceful and inclusive manner.
One common theme is loyalty. Their loyalty to each other as brothers is often explored, whether it's tested by the events in the ninja world or by their own personal goals. For example, in many fanfics, they have to choose between their loyalty to the clan and their loyalty to each other.