Hyouketsu Kyoukai no Eden

A world where humans are invaded by the existence called Yuugenshu. People were able to survive because of the floating continent, Obie Crea, protected by Priestesses' prayers. Sheltis had once aimed to become a Sen'nenshi—a partner of Yumii, his childhood friend and also a Priestess. However, because he fell from the continent to the Eden "Garden of Corrupted Song," he harbored Mateki, what only Yuugenshu have, inside his body, and was exiled from Sophia "Tenketsu Palace" where Yumii lives. Meanwhile, Yumii was hoping for Sheltis to become her Sen'nenshi, but because he fell to the Eden "Garden of Corrupted Song," her wish is still unfulfilled.