Summer is the season for unagi, and Mos Burger has some very special, and very expensive, sandwiches on the way to celebrate Doyo no Ushi no Hi.

Despite having a name that sounds intimidatingly identical to “moss burger,” Japan’s Mos Burger fast food chain has a broadly accessible menu. “Mos” is actually meant to represent “mountain,” “ocean,” and “sea,” symbolizing the chain’s championing of fresh, naturally delicious ingredients.

That accessibility usually extends to Mos’ pricing too, since while it’s a little more expensive than some other chains, it’s still within the budget-friendly range expected of a casual burger joint. However, later this summer Mos is going to be serving up some very premium sandwiches of a sort you won’t see on the menu at McDonald’s or Burger King, and which require a pre-order to get your hands on: an unagi, or freshwater eel, burger.

Traditional Japanese culture holds that the midsummer day called Doyo no Ushi no Hi is when the weather is supposed to be at or near its hottest. Doyo no Ushi no Hi’s exact date fluctuates under the contemporary calendar, but this year falls on July 26. For hundreds of years, folk wisdom in Japan has also said that eating unagi is supposed to help the human body better cope with heat. Some historians say that this idea was first floated by crafty unagi merchants, and modern medical science doesn’t necessarily back up the claim. Nevertheless, the custom of eating unagi on Doyo no Ushi no Hi gained traction, and between unagi already being a luxury food and people now having an excuse to splurge on it for summertime health seasons, demand for fancy unagi foodstuffs spikes annually at this time.

This is where Mos Burger comes in with its Charcoal Grilled Unaju Burger, and if you want to eat it, you’re going to have to shell out 5,800 yen (US$36).

Granted, that price actually gets you two unagi burgers, but since they’re not sold individually, you’re still going to need to cover a bill of 5,800 yen if you want one, and even if you’re splitting the cost with a dining companion, your individual outlay will be 2,900 yen. For comparison, a standard Mos Burger costs 470 yen, so the Unaju Burger is more than six times as much.

That lofty price does get you an elevated eating experience, though, with each freshwater eel fillet individually sliced, skewered, and grilled by an expert chef. The Unaju Burger is also part of Mos Burger’s rice burger family, swapping out bread buns in favor of a pair of lightly toasted disc-shaped rice balls (this is also why the sandwich is called the Unaji Burger, as unaju is a dish of unagi and rice). And since these offerings are too exquisite for an ordinary paper wrapper, they instead come embraced by fragrant bamboo leaves.

The Unaju Burger even comes in a fancy box with an illustrated eel that doubles as the hiragana character for the “u” in “unagi.”

▼ う = u

An arguably counterintuitive part of the deal, though, is that because the preparation of the Unaju Burger is done by experts, they’re not cooked at individual Mos Burger branches. Instead they’re shipped cooked but frozen, and available only through prior reservation. While supplies last, pre-orders can be placed through the Mos Burger website here between June 26 and July 10, with in-store pickup or home delivery schedulable between July 17 and 26.

Source, images: Mos Burger
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