NIC,
Tip: In Japan, everything's
efficient, but nothing's
simple.
Tip: unless you're VERY good at Japanese, always try to find an English workaround.
The site you found, PIA, is a little more complex than it first seems.
Tickets are paid for by debit from a Japanese bank account (common practice, but one you can't do from abroad). Otherwise, it actually appears to require you to open an account (that is, take out a credit card) before you can use it. As a non-resident, you can't do that. Besides, it's a bit of a trick to get young people to apply for credit, which Japanese are reluctant to do except to get a card for travel abroad.
Plug
Green on Red into BabelFish or Jisyo and you may be lucky enough to be able to by a ticket. But you'll need a Japanese address for delivery or the precise location of a Lawon convenience store branch to collect them.
Green on Red operates in cahoots with the promoter
Smash (+81-3-3444-6751, a central Tokyo number), whom, I gather, can speak English kinda, sorta.
Creativeman, the promoter has an
English website. They don't have an English online ticket site, but they often point you in the right direction. There'll be someone there who speaks English, sorta, kinda.
The English-language version of
Time Out for Tokyo is
Metropolis Magazine, and their
concert listings often have English contact numbers.
There are shopping services for English speakers.
This one is written in particularly fetching Engrish. Probably your easiest option.
Many tickets of this kind are actually sold through the ubiquitous convenience store, Lawson. If you're desperate, and arrive in Japan in time, go to the store with a pen, paper and calculator, and engage in some scribbles and sign language. Most Japanese read English better than they speak it, so write everything down. They will help you with the Loppi
automated multi-function ticket machine. I once bought an airline ticket at a Lawson in this fashion.