In the post-apocalyptic world of man and machine, where society "retires" sentient machines out of the need to conserve energy, Ciel is a human scientist who risks her life to protect the machines--Machines who have loved and chosen to grow old, machines who have devoted themselves to science, and machines who were never allowed to be known by anything more than a number.  Ciel left a life of power and privilege to organize and inspire an armed resistance force against an invincible, terrible power which she herself created, and created a Galt's motor type energy system to solve a world's energy crisis, all while making toys for children and wearing pink.

Zero never claimed to be a hero, nor a god of destruction.  He simply put his faith in Ciel, because she was the light that X once was.  In the Megaman Zero series, Zero was Zero, but Ciel was Megaman.