Originally Posted by Tokyoite

An e-ticket number (Document 131-XXXXX) shows the itinerary is ticketed and paid.
for each flight leg "=Flight 1 Day XX, Date XX", if it shows "confirmed", you are ok to fly that leg. Confirm that all legs show "confirmed".
You only need your last name. They will find your reservation using that (unless you have a very common name = Tanaka, Nakata, Kimura etc.)
No ID required to fly domestic legs.
For international travel, same. You need your last name. They will find your reservation using that. They might ask you for the 6 digit reservation code, so just print from the link I sent, show it at check-in and you will be OK.