I recently showed my roommate a video about the origins of metal music. The main take away for this post is that with any musical genre it is hard to point to a definitive moment, song, or band that acts as a hard boundary. For ease of conversation and understanding, you usually pick a few iconic selections to help provide a shared vocabulary but any amount of conversion with other fans will usually teach you that there is rarely a universal standard shared by everyone. Most of this comes from the fact that artists are usually taking in many different streams of inspiration that influence what they do while changes within a medium are usually very gradually incremental even if they might seem hugely iterative on a case by case basis. The major groundbreaking works are usually the accumulation of many other works even if they are not overtly obvious.
What I am saying is often not always a simple straight line of inspiration for anything. But connections can be made if you dig. They are rarely 1:1 affair but tracking major influences are often enlightening to the creation of a work or prove interesting insight into the mind of a creator. I recently stumbled on a pair of characters that made me start a bit of research into who inspired who. Those characters are Boogiepop from the Boogiepop series and Ryougi Shiki from Kara no Kyoukai.
Reverse Thieves 