People who bake know that there are different types of brown sugar. People who eat may know so as well, but for most people sugar is sugar. Most people don't know what caster, demerara, muscovado and turbinado sugar are. The more sophisticated sugar consumer tends to know three things; white, brown, and powdered. I'm no culinary snob so I don't care if people can separate different types of sugars. Unfortunately, my husband is one of the types who knows only the three shades of sweetness previously mentioned. It's dark and sugar, so, it's going to be brown sugar. Yay! Brown sugar! He loves brown sugar.
I'm here to say that kuromitsu ain't no brown sugar. It's a type of syrup that is often used on warabi mochi and other Japanese sweets. It's fine and dandy for various applications, but it's not pleasing to the palate of someone who is looking for that very definable flavor that comes with oatmeal cookies, pecan pie, and spoonfuls of cavity-creating pleasure taken straight from the brown sugar bag. The question of whether or not the flavor pairs well with the white chocolate and wafer combo of a KitKat is also a very valid one.
I'm sorry to say that, having spend 840 yen ($10.63) and having 12 mini bars (69 calories each) on hand, that it isn't the greatest pairing. Speaking as someone who likes the sublime combination of kuromitsu when drizzled over soft blobs of kinako-coated warabi mochi, I was especially disappointed, but not surprised. I think that the bland mochi and nutty toasted soy flour (kinako) are a nifty pairing, but sweet white chocolate is not its friend. It's sweet and intense paired with more sweet and slightly milky.
On top of this being a very so-so KitKat, there is also the fact that it has to be one of the oddest regions to offer a KitKat from. Nihonbashi is a business district in Tokyo. It's not a bad place to go or anything, but it's hardly a heavy tourist district and, as far as I know, it is not really related to kuromitsu. It does relate to the Mitsui family who brought Mitsukoshi department store to Japan so this may be a play on words (mitsu, Mitsui), but it seems a tenuous connection at best. I think Nestle Japan is either trying to hard, or not trying nearly hard enough.