Ayakashi is a metecious form of life, giving unusual forces to the carrier in an exchange on all his life-breath. Yu Kusaka is a student, losing will to live post mortem friend of childhood.

As a child, Yuu Kusaka made a vow upon a shooting star that he would stand on the side of justice and defend the weak. However, the death of one of his friends robs him of the desire to live up to that vow, and he turns a blind eye to the misery of others, using the mysterious power he possesses as a means of making money instead of helping those in need. His days of living only for himself continue, until he's forced to fight for his life against another classmate with powers similar to his. He's saved by a mysterious girl named Eimu Yoake, who also has strange powers. Eimu reveals that his powers stem from a creature known as an Ayakashi, a parasitic being that grants the user special abilities at the price of slowly draining the life of the host. She helps him fully awaken his own. Now aware of the ayakashi he possesses, Yuu must live up to his childhood vow, putting his ayakashi to use and fend off those who would use their own for evil, all while unraveling the mystery behind the death of his friend.—MyAnimeList

One summer night in their childhood, best friends Yuu, Hime and Izumi witnessed anomalous, delightful snow. Little did they know that the "snowflakes" carried otherworldly parasites that bond with children and unbalanced adults, granting them wild card powers along with a debilitating curse. Years later, Yuu and Hime are high school students. Their friend Izumi died under mysterious circumstances two years earlier, an event which led to Yuu becoming the neighborhood pariah. He has psychokinetic powers that are just emerging when an unhinged school bully with deadly, developed powers of his own attacks Yuu and Hime after school. They're saved by Eimu, a new girl who is cold yet oddly familiar. She becomes Yuu's friend, mentor, and protector, helping him learn about the Ayakashi parasites that inhabit their bodies and the secret war that's going on because of them. As super-powered assassins arrive, it's do or die for Yuu.—Anime News Network