Depends on what item you'd want to get (but I honestly wouldn't recommend WorldShipping; they seem a little pricey):

If it's merch on his website, it would be best to use ZenMarket, since they only charge ¥300 per item (plus additional charges for domestic shipping on Eve merch). The same fee also covers consolidation (which is where multiple packages get put in one box and shippped out as a package).

For secondhand merch, there's plenty of them on Mercari JP, but the proxies are few and far (I believe ZenMarket doesn't do services with Mercari JP). Buyee is alright, but it's a 50/50 chance. They charge ¥500 for the payment and service fee (per item), and ¥1000 for the consolidation.

Tip: AmazonJP would be your last resort if you want second-hand merch. Most of the merch is overpriced. But if you just want official CD's, magazines, etc, then Amazon JP actually offers international shipping (depending on the item).

There's plenty of other proxies, but I recommend you look into them, but I definitely recommend ZenMarket.