Speak of the Devil

"It's been tampered with - the section that should have anchored my soul to your body has been altered. How do I put this... In short, we now share a life force."

"What?" said Mo Xuanyu. All the thoughts of reattempting the array vanished from his mind at once. Should he kill himself again, who knows what the Yiling Patriarch would do to him - after all, that's the same as killing them both! His soul would probably be torn to shreds!

"So, if you die," said Wei Wuxian, raising his arm and letting his sleeve fall back. To Mo Xuanyu's horror, four long red cuts besmirched the otherwise pale skin, and they were bleeding so rapidly that his black sleeve was soaked through. "I will die. Vice versa."

(Or: The sacrificial summon unexpectedly failed and Mo Xuanyu found himself falling in love with a very handsome Yiling Patriarch.)