I heard this song a while back and, though it isn't at all popular, it's one of my favorites. Rin's voice sounded so raw and pure in this that I fell in love and knew I had to cover it.
Story: Literal: Rin is a siren who fell in love with a man, and lures him to her with her voice. A little mermaid variant, she gives up everything for him and, after being betrayed and misled, She still continures persuing him, eventually leading him to his doom. Metaphorical: The creator of this song, ayucik, says this song is about adultery. Rin is having an affair wih a married man, and though she knows it will ruin them both, continues tempting him and being tempted herself.
Those are two different ways of enterpreting it. At least that's what I thing anyway. It is all open to enterpretation.
Originally sung by by Kagamine Rin Vocals, lyrics, and subs: Reila Tranlsated by Reila with help from Kannanon