Once upon a time, while standing beneath a shooting star, Yuu Kusaka made a solemn promise to always stand up for justice and help those in need. However, when his dear friend passed away unexpectedly, he lost his motivation to keep his pledge and became indifferent to the pain of others. Instead of using his mysterious abilities to assist people, he began using them to earn money. He lived a self-centered life until another student with similar powers challenged him, forcing him to fight for his survival. Just as he was about to lose, Eimu Yoake, a strange girl with the same powers as Yuu, saved him. Eimu explained to Yuu that his powers came from an Ayakashi, which was a parasitic entity that granted its host extraordinary abilities but also drained their life force. She helped him unlock his maximum potential and taught him about his Ayakashi. Yuu now has a duty to uphold his original oath by using his powers to stop those who use theirs for evil purposes. Meanwhile, he must also uncover the truth behind his friend's mysterious death.