So I'm travelling to Japan for Download Festival. I want to buy tickets but I am unsure if there is a deadline for printing them out (at 7 Eleven). We'll get there less than a week before the event. Is there a deadline for printing tickets?
You should be fine.
While I cannot say 100% that this will be the case since I haven't used Ticket Pia in a while, I'm pretty sure it's the same as the other ticket sites. I was unable to find any warnings on printing deadlines on neither the concert site nor Ticket Pia's site, so they probably don't have one.
I've been to many concerts in Japan, but I have never seen a case where there is a deadline to print the tickets (to pay, yes). You will be able to print the tickets on the day of the concerts if you wanted to. Heck, it's common practice to actually set the limit to the day after, though I assume that's to make sure any procrastinators will be able to print last-minute.
Just make sure you note down the voucher number to claim the ticket, and bring some cash (change), as there will be a fee to print, and they don't take card or electronic money for this particular transaction.
All the major ticketing systems (Pia, eplus, Lawson Ticket, Y! Ticket, Rakuten Ticket) almost always allow you to claim your ticket up until the day after the concert (in case you missed the show but are eligible for a refund), so you should be fine.
7-11 doesn't use their electronic portal for ticketing services like Lawson or FamilyMart do, so you'd show your barcode to the cashier directly. BTW, the ticket pickup charge (店頭発券手数料) is usually set to 110 yen or 220 yen. Make sure you bring some change.