Yoshino Takigawa, a typical adolescent, is secretly involved with Aika, the younger sister of his best friend Mahiro. Tragically, Aika is murdered under mysterious circumstances, prompting Mahiro's disappearance as he pursues retribution. Yoshino moves forward with his life, but everything changes when he is held at gunpoint by a girl and then rescued by Mahiro's astonishing return. The two of them team up with witch Hakaze Kusaribe in order to unravel the enigma surrounding the "Tree of Exodus" and Aika's killer. Despite being exiled, Hakaze seeks their aid in order to avert an impending global catastrophe arising from her brother's selfish desires. Together, they search for the truth behind Aika's demise and work towards saving the world.