Slave to a demon

~*original story with original characters*~
Yoshimitsu is a former royal knight for the kingdom of Vandell. All he wants is to get back into the royal army to defend his country, which is at the brink of war with Kraeoa, a neighbouring kingdom. The ordinary lives of both kingdom's people are slowly crumbling as the tension of war gets more and more great. While wondering during his expulsion Yoshomistu meets a quite interesting girl. Her name is Kuroyami. What he originally doesn't realize is that she is in fact a demon, a creature that was said to only be of legend, but was now proven true. She steals his soul and forces him to be her slave. Him being a loyal and good-intended man struggles with the fact that he's now doing a demon's dirty work, but what other choice does he have? And is Kuroyami really just a heartless demon only out for herself? What will be the fate of the crumbling world when these two team up? Will they let it fall, or end up being the ones who save it?