Chef Mike Han stoops over the butcher block table in front of him and guides a sharp blade, surgeon-like, through the pale flesh of a piece of raw black sea bass that once swam the waters off of Martha's Vineyard. He then wets his fingers before grabbing a small mound of rice, shaping and molding it to match the size of the fish. The two are joined as one, then topped with a bright pink flower and a sprinkling of Amagansett Sea Salt. "I love it when you call me big poppa," Biggie croons in the background.

If that last bit caught you off guard, it's probably because East Coast rap icons aren't traditionally paired with the omakase sushi experience. But the choice of soundtrack isn't the only thing to set Mayanoki, a sushi pop-up turned somewhat permanent restaurant, apart from its bluefin tuna-touting brethren elsewhere in the city. The restaurant has a fierce dedication to serving exclusively sustainable seafood over the 15 course meal it offers twice an evening Wednesday through Sundays.

Co-founders and partners David Torchiano and Josh Arak began the pop-up at Brooklyn Oenology in 2012, first as a once a month special that blossomed into a sometimes weekly event at the now shuttered Williamsburg wine tasting space. That's where they picked up general manager and partner TJ Provenzano, who acts as guide and sommelier at their new home inside a small space owned by neighboring wine bar Grape and Grain. Chef Han came on board in May, spearheading the quartet's vision to make as much of their menu as possible sourced sustainably.

"When it comes to other cuisines, they always promote that they use local beef or chicken, except when you go to high-end omakase it's always, 'We flew this in from Japan' and that's acceptable and I don't know why," Torchiano told me in discussing the concept for Mayanoki. "Delivery chains and distribution are not up to the same standard as they are in Japan, so I think that's what turns off a lot of the chefs here. We just feel it's a challenge we need to take on. While we want to respect the tradition of sushi, sushi has always been about food preservation and by its nature it was sustainable."

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Pacific bluefin tuna, arguably one of the most requested and iconic sushi fish, has seen its numbers depleted by 97% thanks in no small part to its popularity. You'll never see it on your plate at Mayanoki. Instead, the focus will be on smaller local fish. "Our goal is to show that there's no need to serve bluefin tuna or fish from Japan," Torchiano says. "We're discovering what American sushi is," Han echoes.

On the evening the team invited me to see what they were all about, Han was serving seafood including oysters—a note he likes to begin on given NYC's strong ties to the bivalve and their status as a former street food—Sockeye Salmon from Alaska, Long Island squid he'd purchased from Blue Moon Fish in the Union Square Greenmarket, Spanish Mackerel from the North Fork, and black cod from British Columbia, one of two international fish they serve at the restaurant, the other being Arctic Char—one of the most sustainably farmed fish in the world—from Iceland.

Fluke, aged for six days, was dressed in a sauce made from Santa Barbara uni—a species Han admits is on the Monterey Bay Aquarium Seafood Watch's "yellow list," meaning it's not their top choice for sustainability but it's not one they recommend avoiding—and a micro nasturtium leaf. The richness of the sea urchin and natural funk of the fluke are nicely balanced by Han's signature rice, a red vinegar and salt combination that eschews the traditional addition of sugar.

The inclusion of leaves and edible flowers continues throughout the meal, popping up inside of the oyster or draped across a piece of the sockeye salmon. Such additions aren't traditional for the edomae-style that Han employs, but it appeals to his visual art sensibilities. "We want beauty, but it's not simply about beauty," he says.

Chef Han torches some Long Island squid (Nell Casey/Gothamist)

There are only eight seats in the restaurant, which the team renovated to their specifications after agreeing to sublet the space. Provenzano pours local wines, ciders and beers built around the food, which means the list changes as fish come and go from the menu. "The one thing we do look to Japan for is sake," according to Torchiano. "We're hoping to start working with a Brooklyn-based sake producer, but we're currently purchasing Japanese sake. That's the one thing that we're using that's not local."

Regular omakase diners are used to being face-to-face with the chef, but Mayanoki has removed the usual barrier wall between the two, creating an intimate experience where you feel like you're sitting at the chef's cutting board. You're front row when Han whips out the blowtorch, to puff up some squid or add char to butterfish, which is brushed with a buckwheat honey soy sauce reminiscent of an unagi (eel) preparation.

Han finds little nods to flavors and presentations that are more familiar, and anyone skittish about eating a fish they've never heard of will be put at ease by the team's amiable personalities and excitement about what they're doing. "There's a lot of talking," Torchiano says. "We try to be very laid back; we want to serve the best quality but we want it to be approachable."

"We're just letting people know there are literally other fish in the sea," Provenzano concludes.

620 East 6th Street; Meals are 15 courses at $95 per person, with two seatings (6:30 p.m. and 8:30 p.m.) Wednesdays through Sundays.