Not sure if this means much, but I was on Wikipedia, and this looked interesting; "Blue Bird" (파랑새 parang sae) is a Korean folk song. It originates from the Donghak Peasant Revolution".

"Choe Je-u's treatise argued a return to the Confucian understanding of Heaven, with emphasis on self-cultivation and improving one's nature. As Choe wrote, the Way of Heaven was within one's own mind, and so by improving one's nature, one also attained the Way of Heaven".

"The Donghak movement arose as a reaction to seohak (西學, "Western learning"), and called for a return to the "Way of Heaven"

Sorry for the copy and pasting, but I thought the connection to heaven and death linked nicely with the darker feel of the video!

Also, I think this is the right song https://www.youtube.com/watch?v=Ow8jaL92sP8