A world in which one's happiness and misfortunes, even their lives are controlled by "luck"... In this world, there are three identical looking people in existence. Each of these three split between them an energy-like force called "Tera." This energy can be attributed to the amount of "Luck" or "Life Energy" that an individual possesses.rn
And between those three, the one with the largest share of Tera is called the "Root" and the two possessing a lesser amount are called the "Sub." If a "Sub" should ever meet up with another person that looks just like them, they would die. Their Tera would then be absorbed by the remaining two. If two "Subs" should run into each other, they would both perish, leaving the entire amount of Tera to be absorbed by the "Root." That individual would then become a "Master Root" and come into possession of an enormous amount of luck and lead a life with success at every turn. This is the hidden truth of existence in the World of Humans and is called the "Doppeliner System." In accordance to the rules of the Doppeliner System, there exists beings who observe the human world, maintaining the balance of Tera, known as the "Coexistence Equilibrium." These beings possess ability that surpass that of a normal human being, and reside in hiding in places known as the "Pure Place" in tribes. They are called the Tera Guardians. This is a tale of battle that begins with the meeting between a human boy named Keita and a young Tera Guardian girl named Kuro...