In the peaceful little town of Sakuranomori, a group of young friends are about to bid farewell to one of their own. Due to his parents’ business plans, Sana Hidaka has to move away from his quiet childhood home to the boisterous city of Tokyo. Though it pains him, he must say goodbye to his precious friends—the kind-hearted Aoi Oribe, the spunky Wakatsuki twins, Shuri and Shuusuke, and the cheerful and upbeat Nanaka Yatsushiro. But even though he is reluctant to leave them behind, he believes that no matter how far apart they are, they will always cherish the memories of their friendship. Five years later, Sana, now a 16-year-old high school student, returns to his hometown with the hope of restoring his old life. However, he quickly realizes that although his town may not have changed drastically, the friends he left behind are not who they used to be. Unsettling shadows loom over Sakuranomori as his friends hold new secrets and bear burdens that threaten the bonds they once shared.

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.

The Sablum Empire has been attempting to take over the kingdom of Windland for many years, and are now plotting with the mercenaries Sister Hell and Darkness Knight to start a new offensive using powerful magical beings called Angels. Hyaweh, a carefree yet talented swordsman, and Priecia, who just might be the lost princess of Windland, are enrolled at the Knight's Academy in Windland to hone their skill at swords and sorcery. There they meet many friends and allies who can help them protect their homeland from the impending invasion.