My top three Japanese bands:
Metalucifer - old school heavy metal, stupid lyrics and silly image. Get Heavy Metal Chainsaw if you're into classic metal.
Sigh - psychedelic metal mixing film music, handclaps and pretty much everything else. If you listen to Solefald you'd probably appreciate Sigh as well. Get Hail Horror Hail. The first albums are rawer and not as experimental.
Volcano - power/thrash with leads heavily inspired by In Flames. They have two albums out but I've only heard the first one, Volcano.
NP: Theory in Practice - The Armageddon Theories