Mara, often short for Mara-Papiyas, is the lord of the sixth heaven of the Desire Realm and the head of gods in Mount Meru. It is said that if a man could reach beyond the sixth heaven, he will then overcome all kinds of desires and delusions to go on the path to enlightenment. So there is only a line between the Buddha and the devil!
I get the feeling that Licht is the duchess's future child, who also probably got separated from his mother like Nanael was. Gosh that timeline was brutal for both of them