Maybe Sasuke teaches him the Chidori in a moment of camaraderie. And for the Rasengan, it could be an older and wiser Naruto from the future who travels back in time to teach his younger self.
It's not based on a true story. The plot and characters were invented by the writers for entertainment purposes. There are no real-life equivalents or incidents that inspired it.
Definitely not. The vanishing of the sun is a concept usually found in science fiction or fantasy, not in reality. There are natural processes that govern the sun's existence and behavior, and vanishing is not one of them.
In many fanfictions, Naruto might master the Rasengan through intense and unique training methods. Maybe he gets some special guidance from an unexpected source, like a hidden shinobi in the village who has a different perspective on chakra control. This person could show Naruto some new ways to focus his chakra, which finally enables him to form the Rasengan successfully.