Gaara is sometimes a significant character. His unique powers and his friendship with Naruto could lead to him being involved in the fight against Madara. Hinata might also be present, showing her support for Naruto in different ways, like using her Byakugan to detect Madara's moves. And then there's Itachi, whose complex past and powerful abilities make him an interesting addition to the Naruto vs Madara scenarios in fanfiction.
Sasuke is often a popular character in these fanfictions. He might play a role in helping Naruto against Madara or have his own motives during their battle. Kakashi can also be a prominent figure, perhaps using his Sharingan in a crucial moment to assist Naruto. Another popular character could be Hashirama, as his connection to Madara is a key part of the original story and can be further explored in fanfiction.
Naruto. His incredible chakra and never - give - up attitude make him a force to be reckoned with. He could be the one to deal the final blow.
Sasuke could be a main character as well. Given his own experiences of being an outcast and having a thirst for power at times, he could relate to Madara in some ways. They might form an unexpected alliance or have a rivalry based on their shared experiences of feeling neglected or misunderstood in the ninja world.
Konan could be really interesting. In some fanfictions, she might have a different backstory or motivation that affects the Naruto vs Pain fight. For example, she could be secretly trying to stop Pain from going too far in his destruction of the Leaf Village.
Naruto himself could still be a main character. His relationship with Madara's reincarnation could be explored, like how he tries to understand this new version of an old enemy and whether he can trust him or not.
Obviously, the heir of Madara would be a main character. There might also be other characters from the original Naruto series, like Naruto himself. Naruto could be in opposition to the heir, seeing them as a threat to the peace he has worked so hard to achieve.
Obviously, Madara himself is a main character. He is the center of the story's legacy aspect. Naruto might also be a main character as he often represents the new generation and the hope for change in the Naruto universe. He could be the one to either oppose or understand Madara's legacy in the fanfiction.
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.
The 'forbidden love' trope also often plays a part. Since Madara was once an antagonist in the Naruto series, their relationship in the context of a mpreg fanfiction can be seen as a forbidden or unexpected one. This can add an extra layer of complexity to the story, as they navigate not only the pregnancy but also the social and moral implications of their relationship.
One interesting plotline could be Naruto discovers a new form that gives him an edge over Madara. For example, a form that allows him to nullify Madara's Sharingan abilities. Another could be Madara having a change of heart due to Naruto's unwavering belief in him. Maybe he starts to question his own motives for destruction.
Sasuke could be quite popular. His complex relationship with Naruto and his own power could add interesting dynamics to the fanfiction. For example, he might be jealous of Naruto's bond with the Kyuubi at first but then come to understand its importance.