I'm a Useless Woman, How Did I Become the Demon King's Fate?

Secret agent to poisoned noblewoman in one breath—then thrown on an altar beside a half-dead stranger. To survive the Crimson Flame toxin, she takes one look at his godlike face and paralyzed body, grits her teeth, and forcibly 'heals' him. Only later does she discover he's Ye Xuanling, the infamous Ruthless King known as the Living Yama. She thought she'd use him as an antidote and vanish, but fate has other plans. By day he's the cold-blooded prince who commands armies; by night he slips into her chamber, cheeks flushed, whispering, 'Xixi, my Black Ice Gu is flaring again... please, let me s…