By request, the Burger King KURO(black) diamond.

After seeing the ad for this, a friend of mine out of country asked me to try this and report back. I have seen some pictures of the ad circulating around online and popping up on my facebook feed, so I thought I would take one for the team and satisfy everyone's curiosity.
When I went up to the counter at bk, the first thing the lady recommended to me was to try one of these burgers. Looking around the store, I was interested to see if other people had ordered it, but a quick glance showed that only a couple customers had the black wrappings on their tables. This was the day after the KURO burgers went on sale, so maybe everyone who was really curious ordered it on the first day.

I ended up getting the KURO diamond, which basically is some standard mayo, onion, lettuce and tomato added to a black bun, black cheese, not-so-black patty and black sauce (the other offering, the KURO pearl doesn't have the veggies and costs 480 yen). I paid 690yen for the KURO diamond and a L coke zero, so as far as fast food goes, this was not cheap (the burger by itself is listed as 690yen and comes with a 'free' large coke. They even advertise the 'coke combination' at a higher price and strike it through as if they were offering a discount).

For the bun and cheese the black colour comes from the addition of burnt/charred bamboo, while the sauce, an onion and soy-based concoction, is flavoured and coloured by means of squid ink. The patty is perhaps grilled a bit darker than the regular patty, but I couldn't tell too much of a difference as I hadn't had a meal at BK in quite some time.

The burger came nicely wrapped in a black sheet. Taste-wise, it was... underwhelming. This is not to say that it was bad, but from its appearance, I had been expecting something much more strongly flavoured. The bun and cheese were slightly smoky tasting the cheese was actually less salty than the usual fast food offering. The patty was grilled well and perhaps a little bit larger than the regular patty, but nothing to write home about. The strongest taste came from the sauce, the soy-sauce taste with a hint of squid flavour. They call it a shalyapin sauce- it reminded me a bit of oyster sauce in some respects. The most interesting flavour was that of the sauce, and I could see it being a good match for an eggplant and meat stirfry. The taste of the burger as a whole was good, if lacking in the impact department.

Overall, the KURO diamond was not bad... not as salty as your average fastfood item and interesting to look at. I wouldn't expect it to sell that well due to its relatively high price and beyond interest in it as a novelty item (and likely  marketing tie in with coca-cola), as a menu item I would say that it has limited appeal and is unlikely to attract repeat customers.

See BK Japan's campaign website here:
https://www.burgerkingjapan.co.jp/campaign/cp123.html