I'm quite familiar with donki and that saccharine jingle, but never found them to be much of a supermarket in Japan. They had roasted sweet potatoes, cheap oolong tea, and a bunch of foreign products, but mostly were filled with made in China crap like bdsm halloween costumes, and fake Rolexes.

Though, if you say their overseas locations are more supermarket than tchotchke vendors, I should check them out.