Is Edermask based on some legend?
It seems that several of the other characters and key story points are based upon Greek mythology.  All though this has not been confirmed by the author himself yet.

There is no actual figure in Greek mythology called Edermask/Ethermask/Nenomius, the antagonist Janus does seem to have a Greek counter part. janus, the god of beginnings and passages. Is said to be a 2 faced god. One facing the future, and one facing the past. 

This god would fit the image of both the characters as their looks are identical, and behaviour matching that of this particular god. One can not let go of the past, and one only wishes to move forward (very, very roughly transcribed).