possible to buy airplane ticket in Japan

My question is, is it possible for me to buy tickets in japan and uste them in mexico? i mean, my girlfriend and i have more than a year living together in Mexico, she is working here as a japanese teacher, we would like to visit her mother next december, but here in mexico tickets are amazinlgy expensive, her sister offered her to buy the tickets in Japan dor us here.. is this possibe??

It's most certainly possible but I seriously doubt that there's any difference in price between the two regions. At least no difference significant enough. In this age of e-tickets though, it's not a hassle at all.

I have done it the other way around: I have bought tickets in Paris for people leaving from Japan as I could get much better prices in Paris at the time. When ordering the tickets I just mentioned the itinerary and sent my friends the tickets via airmail.
If you can get the tickets cheaper in Japan, I would certainly use this option.