Girl meets Robot. It's as simple as that.  

Eunhyuk is a monster. Donghae is his prey. But not everything goes as it was planned, and the prey isn't as easy as Eunhyuk had predicted. Caught in the human world, what will happen to the soul devouring demon and his newly found "master"?  

"And so, the devil found himself a human girl, to make her his one and only unwithering flower."