User blog comment:Sorairo/Song Analysis/@comment-4010415-20130829063214/@comment-15108745-20130829222106

I'm pretty sure day and night is a comparison to light and dark as well. I can't say exactly what it means because the show's only just established the main cast and hasn't progressed to dealing with the bigger problem.

I sort of think it's like the severing of the head of the Forest God in Princess Mononoke. Life and Death coexisted within one being and then when the head of the god was severed, death ran rampant. So I imagine that there was some natural presence of darkness (night) in the world of RWBY and that it was let loose (severed). This could possibly be the origin of the Grimm. But.....no one knows for now.