There is a world that some would call Heaven, populated by beings known to humans as Immortals. They have been tasked with a simple charge: protect humanity.

Ryoki didn't know or care much about this world; she had typical problems to deal with, like school and home. But someone is watching her, one of the Immortals: Haeilios, Ryoki's protector. He reveals to Ryoki a world far more complex and dangerous than any she has seen before.

He is something difficult for Ryoki to comprehend, but at the same time, Ryoki is an anomaly to Haeilios as well. In more ways than one he has never protected someone quite like her. Can he keep safe what he does not understand? Or will she break through his Aegis and face these dangers directly?