| This article is based on data from a Japanese-only game.|
The following content has not been released in the English language, so details are subject to change at any given time.
Thanatos was a reaper from Ratio who fell in love with an unnamed human woman while reaping souls from Naraka in order to sustain Devaloka. Rumors began circulating that he was visiting Naraka during his off-duty hours, which eventually resulted in him being banished from Devaloka and leaving it altogether in order to protect Naraka. His brother, Hypnos, was also a reaper and was reassigned due to this incident, becoming the general of Ratio. Thanatos and the human woman produced many children, the Grigori, passing down Thanatos's blood and bestowing upon the offspring powers similar to Avatars. The Grigori's appearance does not differ too drastically from that of humans', though they do all look very similar to one another.