Thanatos is a collective name for the spirits that resemble masks who serve The Echoes of Mavolia. They followed Anise, Stroud and Dragon Emperor Drakonis at one point in time and crowned each of them as Archdemon of Mavolia (Anise after creating Mavolia, Stroud after "killing" Anise and Drakonis when Anise died for real). They turn all who are touched by them into Grimslies/Mavoles. They are only seen directly in Dawn of Mana.