Mint Yokohama just celebrated its 15th Anniversary and it is now the only store in town.
Located just a few minutes' walk from Yokohama Station, for those in the area it's pretty convenient. They have a pretty good selection of the usual suspects. Of course, they'll have current packs and boxes for major sports releases in Japan and abroad, including a very large soccer collection.
Because I didn't really look much in those boxes, I can't tell you for sure what's inside yet. I'll have to update this post sometime when I get more details.
I haven't tried English at this store yet. It's on my "to do" list for my next visit. They didn't try English with me, though, speaking only Japanese. I understand enough to get by without English, which makes testing this a bit tough! As for customer service, Japanese store clerks are generally very polite, and card store employees left me alone until I was ready to purchase, after which they were as I'd expect here.
The store is open seven days a week 11:00-20:00 with no regular holidays. Phone: 045-316-1710; Japanese address: 神奈川県横浜市神奈川区鶴屋町2-20-1 YTUビル2階. Store's homepage (in Japanese).