Maybe an orphan from a non - Uchiha clan who has a special ability that Madara finds interesting. This character would be malleable and eager to learn from Madara, as they have no other real family or guidance. They could bring a fresh perspective to Madara's teachings.
Yu Zhouzhou's last words in " Hello, Old Times " were: " The old times at the end, and the hand that held me tightly. In my old times, he was the light."
In this fanfiction, Naruto's character development could be seen as a counterpoint to Madara's. Naruto is all about hope, friendship, and protecting the village. Madara has been through a lot of pain and betrayal which led him to a path of destruction. If Naruto is like Madara in this fanfiction, his development might involve a struggle between his own beliefs and the allure of Madara - like power and ruthlessness. However, Naruto would probably still find a way to use any new - found power in a more benevolent way compared to Madara.
Well, in such a fanfiction, it might start with Naruto being in a situation where he becomes Madara's pet. Maybe at first, Naruto is defiant but as time passes, he could start to understand Madara's motives in some strange way. Madara, on the other hand, might initially see Naruto as just a possession but gradually develop a sense of attachment. It could be a really strange and complex relationship that unfolds as the story progresses.
In a Naruto fanfiction where he has Madara's attitude, he could become more power - hungry. Madara was always seeking power to reshape the world according to his ideals. Naruto might start to view the tailed beasts not as friends but as tools for greater power. He could try to gather more chakra and perhaps even attempt to unlock new forms of power that are more in line with Madara's dark and ambitious nature, which would shock his comrades and enemies alike.
Well, it depends on how the fanfiction is written. He might have some of Madara's basic powers like the Sharingan, but perhaps in a more evolved form. For example, Madara's Sharingan had different levels of power, and his great - grandson could have a Sharingan with new abilities that are unique to him.