A service that helps you bid for the item. Have it shipped domestically to them and then shipped to you. Since yja only ships domestically.
One that I use is buyee.jp. Instructions and how to are all listed in the Faqs/help pages. So everything you need to know to get started will be there. They're fairly simple to use.
Some others would be tenso, shoppingmalljapan, rinkya, etc. I don't know much abt their usage but I'm sure other members will chip in. Instructions for their usage are all listed in their website as well. Anything you need to know on how to work these proxies are all listed on their faqs.
I don't have much experience with winning an auction so these are just my 2cents.
I'm sure there'll be others way more experienced to help you with it. Feel free to pm me about buyee.jp's usage.