How are demons going to become humans? They can't even reincarnate, plus he ages as a human (he's like a chimera rather). The cursed land only magicians go to obtain more power (nothing more), he went there to obtain more power and everything went wrong and he got the devil, that thing is influencing something that already felt "ENVY", to take full possession of his body
So basically he was human to begin with but was possessed by the demon? But he died
yes, it is like a doll that they made to be the container of the demon, but Evan had his own mind, conscience and that (he was a different being). When he went there to seek power, he put that thing in his body for now, he does not have total control of his body but the demons tempt humans to allow themselves to be controlled
I'm thinking when she defeated the demon he turned into a young boy who is Evan so wen she disappeared and Evan went to that evil land, the demonic being in him woke up. Wat y'all think?