It is the key to the creation of the world, and he is the son of God who escapes the world. It is a tool for traveling through time and space, and he is its master.
The reason why she returned to ancient times was very simple, just to realize her thousand-year-old love. She wants to be with him. But her time travel brought alien objects and the invasion of future humans.
Obtaining the power to travel through time and space and change history is no longer a dream. Anyone can become a god who creates a new world. History is changing all the time. So she can only choose: to fulfill herself and destroy the world; or to wrong herself and make history complete.