In this world, there are three identical looking people in existence who split between them an energy-like force called “Terra.” This energy can be attributed to the amount of “Luck” or “Life Energy” that an individual possesses. There also exists beings who observe the human world, maintaining the balance of Terra, 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 Terra Guardians. This is a tale of battle that begins with a chance meeting between a human boy named Keita and a young Tera Guardian girl named Kuro.

Keita Ibuki is a computer programmer who, with two of his friends, is developing and trying to sell a video game program. He has a chance meeting with a high Mototsumitama named Kuro. He gives her his dinner, a bowl of ramen, and tries to protect her when she is surprise attacked by another Mototsumitama. He loses his left arm, but she exchanges it with her left arm (Mototsumitama have enhanced healing ability).