I Get Questions: History of Idol Metal

Jaxson in the comments writes:

I have a question for you (perhaps a bit of idol trivia as well). Who did the first idol/metal collaboration you heard of? For me, it occurred ten years ago.

I thought this was really interesting; for the more well-schooled and well-seasoned (read: OLD) among us, to where can we really trace the history of idol metal, including animetal? What was already in the water in 2010 that gave us Babymetal, BiSH and the HKFCapalooza, that made people think that harder sounds and idol could mesh? This question is specifically geared toward the metal side, but any clear point of origin is welcome.

Answer away in the comments! These comments! The ones below!