Manga Like Godspeed

Long ago, there was a great war between the realms of angels and demons over mankind. The demons were a wicked lot and treated humans as their toys, while the angels fought to protect humans from the demons. When the war was over the angels built a town called Ilvia to keep humanity safe against the demons. In the middle of Ilvia is a place called sanctuary where children live under the guidance of the angels. The angels teach the children they must not leave the sanctuary because the demons will get them due to being attracted to their pure souls. When the children reach there fourteenth birthday they graduate from the sanctuary and are seen off by the other children to paradise. What is paradise? All is well or is there something more sinister going on behind the scenes...