As a guitarist I have noticed that j-rock doesn't seem to proliferate with shredders. I'm sure there are any number of Japanese super-fast players, but they seem to be very much "musicians' musicians" rather than feature in the most popular j-rock bands. Flashy guitar solos don't abound in j-rock (... strange really that I'm attracted to the music, as I am a real $ucker for flashy solos! XD)
Anyway, my recommendations are:
Galneryus, and Aushvitz (those bands both have the same guitarist, Syu; he is really good.
)
Aikaryu (not all of their songs have guitar solos, but those that do, have some nice shred).
Kagrra, (some nice duel-guitar stuff goes on in their rockier songs).
Crosshard (guitarist Takayoshi Ohmura plays some HOT HOT stuff!
)
Penicillin (again, not shred in every song, but when they do it, they do it WELL!!!)
B'z (poppier light rock, guitarist Tak Matsumoto is one of the most versatile and best-known).
Merry (not flashy, but tasty blues-rock guitaring with a nice tone).
D
Scissor
Girugamesh
Deathgaze
KuRt and La'Mule have some nice stuff too.
Die and Kaoru from Dir en grey are overrated as guitarists. Sorry, but they are. I'm NOT saying that they're not good. They clearly ARE good, just not as AMAZING as is made out. Dir en grey are a great band, but their strength lies in their COMPOSITIONS, not in the 'shred factor'. However, Die's pinch harmonics own.