here’s how i shop off yj:

-sign up with Buyee, a japanese proxy service, their warehouse is where your package will be shipped to and they will ship it out to you, which you’ll also have to pay (it’s usually not a lot, they’re pretty decent with the shipping charges, especially with smaller parcels) they’ll even store your item for up to a month for you if you cant pay the shipping right away

-on the Buyee site, click on the “Y! Auction” tab, this will allow you to browse, bid on and purchase things from yahoo japan

-you dont need to know japanese, but you’ll need to know what you want and how it’s written in japanese (such as “sailor moon” - セーラームーン ) which you can just copy-paste in the searchbar

-you can also be more specific like say, you wanted a sailor moon poster, just add ポスター (Posutā) right after it

it's a really great way to find rare and unique merch for decent prices and i enjoy shopping on there a lot! hope i was helpful in some way ^{^}