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.
Another theme is redemption. Sometimes in these fanfics, Madara has a chance at redemption through his fight with Naruto. Naruto's belief in people's goodness can influence the outcome in such scenarios.
Luffy from 'One Piece'. Luffy's rubbery body and his determination are similar to Naruto's in some ways. In a crossover, Naruto in KCM could help Luffy take on stronger foes, and Luffy could show Naruto his carefree yet strong - willed attitude.
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.
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.
One common theme is power exploration. Writers often focus on how Naruto can further develop and utilize his KCM powers. Another theme is self - discovery. Naruto discovers more about himself through his experiences with the KCM.
Power exploration is a common theme. Since KCM gives Naruto a huge boost in power, fanfictions often explore how he uses it, and how it changes the balance in battles.
Well, one possible outcome could be that Naruto and Sasuke manage to defeat Madara through their combined strength and newfound powers. They might use their signature jutsus in a coordinated way that Madara can't counter.