Best drama I have ever watched so far.

My review will be very simple:
Visuals 10/10
OST 10/10
Story 10/10 - unlike some dramas, the plot is consistent and it does not get boring while nearing its end.
The demons are completely unlike in any other dramas.
And the most important for me, it is a really beautiful depiction of friendships of different sorts - and their value in life.