When the world's surface collapsed, the city of Novus Aether remains suspended in the sky, sustained by the prayers of the Holy Maiden. Long ago, when her prayer was cut short, a catastrophe known as the "Gran Forte" erupted, tearing the land apart and dividing the lower city into two, separated by a deep chasm. Over time, the lowest level became a refuge for outcasts and those who had lost everything in the "Gran Forte," earning it the name "Prison." But now, a mysterious illness that causes people to sprout wings has swept through the city, prompting the formation of a specialized unit to handle the afflicted quickly and decisively. Among the residents of this "Prison" is Caim Astraea, a former assassin who now takes on freelance odd jobs for his friends, avoiding any tasks that involve taking lives. While working on a job, Caim discovers a girl infected with the wing-disease, surrounded by a glow that brings back memories of the “Gran Forte” from years past...