First of all, the story is so deep and meaningful. The stories and backgrounds of the individual characters really bring out the fact that everything starts from ones heart, whether it is caused by internal factors or external factors. There were so many twists in this drama that it kept me wanting to watch the next episode with deep anticipation. This show emphasized the darkness and holes in ones heart and i find that really meaningful. Next the acting. Wow i was really surprised behind the emotions portrayed and it was as if I could almost relate to the character. Self blame and self sacrifice was really brought out with the aid of the actors. Hwa pyung and choi yoon both displayed self sacrifice and was so much willing to sacrifice their own lives for another due to guilt and friendship. I felt like the cast was really on point and it was as if perfect. The music also played a huge part in the emotional scenes. The slow and soft melody created such a heart wrenching scene that i almost cried along with the characters. This drama has both great plot and so many unexpected turn of events that i find myself getting surprised again and again. I believe I will watch it again soon myself. I will admit the effects and gore are a little scary, but they really bring out the evil and represents the darkness in people's hearts really well. This is one of my favourite dramas that got me so hooked to the story. Guaranteed an engaging watch!!