I keep getting the same question from my Japanese readers: REさん、日本の音楽の中で、どれが一番好きですか？(Mr. RE, what is your favorite type of Japanese music?) Do listen to a fair amount of Japanese rap nowadays, but my favorite genre will always be Japanese metal.
Like most American aficionados of Japanese metal, my first exposure was X Japan's Blue Blood album. X Japan was a quintessential band for many reasons -- they dressed like the ill-gotten children of a one-night stand between Guns and Roses and Culture Club, their frontman hide met with a very Michael Hutchence end, their sound was very reminiscent of speed metal classics, such as Ace of Spades and Kill 'Em All.
During the heady days of Napster, when peer-to-peer sharing was really hitting its stride, I was able to sample a large portion of the Japanese metal genre. I also spent a summer in undergrad in the Kansai area, which afford me the opportunity to go to a bunch of concerts for relatively cheap (Japanese bands love to see Western fans in the audience). I would have to say my favorite band out of the genre is the now defunct speed metal group Sex Machineguns (yes, the name is a play on the Sex Pistols).
Their music videos are particularly interesting, check out this video for the 1997 hit "Burn":
And before I get a handful of quizzical e-mails asking about the guys in black jumpsuits running on treadmills and pounding mochi, I don't get it either. They show up on some of their other videos as well.
Update: I would be completely remiss if I didn't mention SEIKIMA II and their groundbreaking 1987 music video for "1999 Secret Object."
These guys are probably the most hardcore of any Japanese metal band. Like KISS, their make-up remained relatively unchanged for two decades. They also made good on their promised to break-up on December 31, 1999 and have stayed disbanded for 7 years despite popular pressure to reunite.