You can walk up and buy a ticket for most games, especially the more expensive seats. I never had a problem. There are exceptions of course. Giants will sell out, but I also advise you not to go to their boring stadium.

I even bought Swallows-Giants playoff tickets online the day before.

Ha, if you check the website he warns that he can't get tickets for special games. So essentially he is just a local individual who charges $59 to buy tickets online or down at the local convenience store. The value of a ticket service should be to get tickets that are hard to purchase.

Once you get to Japan, I recommend Ticketport. I used to go my local one, which is in the 109 Bldg. http://www.shibuya109.jp/en/s/ticketport_piastation/ They might know a few words of English. One advantage versus a convenience store (and you will struggle with the machine) is that you can pick specific seats from seating charts. Their fee is only 105 yen per ticket. I used Ticketport for football tickets because they discount them if you buy them in advance. Never saw the need for baseball, but if you want to be certain then it's a good place.