Yes, I bought the ticket online through their website.
http://www.fighters.co.jp/ticket/
I'm sure I used google translate to navigate the website and purchase the ticket.
I just looked at their site again and unfortunately I can't replicate the ticket purchase process now. I think you have to click on "seat view" and then "purchase." That may prompt you to create an account with them before you can purchase the tickets.
If I recall correctly, they offer different options for ticket delivery, and one option was by QR code. That's what I chose. I bought the ticket, gave my credit card number, and they emailed a link to the QR code. Then I just took my phone with me to the game and pulled up the QR code and showed that at the turnstiles. They scanned it and I walked in, not unlike using a mobile boarding pass to board an airplane.