The Demon Lord was crying for the original host? He should have been the ML then, he's dark, his body looks like fluffy rainy clouds, looks kinda mischievous and appreciative, kinda crazy as well so spiciness wouldn't lack, it'd be funny, idk. XD
Btw, being serious, she shouldn't trust him that easy, he gave her a fishy skill, a sick body full of pain and if she died in her past life there's no way she'd be able to come back (unless ofc her body is in a coma or something). Anyway, he's a demon, how trustable he can be? xD