Shangguan Qian x Jiang Guwon [AU]. [My Demon x My Journey To You]
Story:
Shangguan Qian is a secret powerful assassin/demon slayer sent to weaken the Demon Guwon. She seduces him as she portrays herself to be a kind, beautiful lady hiding her true predatory intentions. The cold demon falls in love with her and with his guard down, she's able to debilitate him with little hesitation. She pretends to be heartbroken after his demise; but he comes back to life anyway. And even after her betrayal, his heart still isn't willing to let her go.