Jun at JapanTackle has the best English and is very helpful.
Asian Portal has the best prices+ free shipping, and toughest website to navigate.
I'll add Plat to the list - very pretty website, and a great place to follow for rods, though again, part of the trick is identifying what they have in stock. They're very good about checking and ordering stock from manufacturers, and won't send you a purchase invoice until your order is squared away. Plat also provides reel repair parts and schematics.
Hedgehog Studio is the place to find every reel tuning part, and always the fastest to ship out.
I've shopped in Japan for as long as the internet has been around. Japan websites aiming to the US market is something relatively new, and because of Japan banking laws combined with the language barrier, at one time, you could only buy through brokers. Noppin.com and ZenMarket are two good brokers if you want something from a Japan website that doesn't cater to USA shopping. When I bought XUL and UL rockfish rods a dozen years ago, even though they came from a Rakuten store, Noppin shipping made it better and cheaper to order through them.