I don't have a lot of knowledge of Japanese hardcore, but I know that Bastard's Wind of Pain is one of the best examples of it. Wind of Pain rages for its full duration (just under 17 minutes). My favorite parts include the first riff in "Never Change," the opening riff in "To the Stumped Underdogs," and the final minute of "Truth." Thanks to John from Weekend Nachos for turning me onto this awesome band. The first two songs posted from WN's new LP are on a total Bastard tip, so check those out. Hopefully, they play some Bastard covers in the future.
Get it here!