Japan has notorious laws regarding any substances - any vendors that ship to Japan? LSD or MDMA, the former probably (supposedly) being safer.
I searched but only found one thread from ~5 months ago with no real results, but perhaps this will yield more info.
General disclaimer: well aware the risks etc etc etc.
Tesselated shipped to Jordan, don't see why they wouldn't ship to Japan. I would stick with the LSD, even at Tess prices you could 20x your money and get mad kuchi-san from dem jap honeys.