She Was Both Called God, as Well as Satan

In the distant future on Earth, there was a girl with God-like powers. That girl is the last survivor of the former human race that flourished in ancient times. The Ancients. And on that very same Earth, a new breed of humans with the ability to wield Magic emerged. That girl began to observe the new human race silently. Sometimes called a God, other times called Satan, that girl continued to observe the new human race. This is the story of the happenings between the lonely girl and the hardworking new human race. — Description from novelcodex.org