Take Me In, My Lord

I'm the daughter of the leader of Lingji Sect, a top killer organization. Though I'm not good at killing people, one day a strange man came to me and asked me to complete a mission for him. Strangely enough, he said I was the only one who can do the job. That is, to steal a secret letter from the man himself! Only it was the "him" from 10 years ago. Who exactly is this man? What does his future have to do with me...