As old as time the stories goes, a devil and a god were wedded to each other. Their union, however, was as ill-received by the divine as the debilish, and thus began one of the very first holy wars. Years passed and so did centuries, and as it came to an end it all, the side of gods murdered the she-god, but the devils? They had a creed as they fester on abundant corruption, in their unity against threats to both living and the dead, thus killing Asmodia would only cause more trouble than it was worth, as her soul as a devil would land in the infernal regardless.
'So sleep, until a god decrees your awakening.' Those were the words she last heard before her own kind cursed her into an eternal sleep. Or at least it should've been eternal had Athenia not awakened her from her slumber.