Akaiito omakase a diamond in the rough

Finding great Japanese dining where you would least expect it is part of what makes it great to begin with. Both Minamishima, our three-hat temple of finely sliced fish, and Tempura Hajime in South Melbourne are buried inside unlovely office blocks. For food fans, finding that diamond in the rough is as good as it gets, and a million blogs, books and TV shows are dedicated to the hunt.

But then there's Akaiito. Opened in May on Flinders Lane, it is, by its own words, a contemporary Japanese fine diner, and the prices it charges support that claim. So when you hear that its premium offering is a $115 robata omakase experience – a 13-course epic of sushi and things from the grill, which needs to be booked 24 hours in advance and can seat just a handful at a time – there seems to be no mystery. Surely this is a diamond hiding exactly where you should expect it.

Then, you arrive. This isn't the buzzy patch of Flinders Lane precinct, but the western side of Swanston Street, in the building that used to house Bluestone Restaurant. Early for my 8pm sitting, I'm ushered downstairs to the cocktail bar where, against a backdrop of timber beams, heavy stone walls and black and lipstick red furniture that's already showing wear, a smattering of workers are exclusively drinking bottled beers. Whether that's down to the beer taps not working (a problem unfixed for weeks, the frustrated bartender tells me), some wines being marked up by 300 per cent (the 2016 Leeuwin Estate Prelude Chardonnay, selling here for $20 a glass, is $34 a bottle retail) or the cocktail list being largely vodka and sugar-driven, is unclear.

But it is fair to say first impressions aren't strong. The bartender promises table service, then forgets. And while I'm sure a lot of money has been thrown at the fitout by hotel-focused design company HBA, the veneer feels thin. Latches on the toilets threaten a lengthy sentence. The open cellar is mostly bare. The restaurant's main feature, a "red thread" shaped like a luminous strand of DNA, has a chintzy plastic sheen.

Had I not secured my booking with a credit card, I might have left when the DJ moped his way downstairs to change from one house track to another. But I didn't. And I'm glad.

There are only a few seats at the dark marble omakase bar in the upstairs restaurant, but much like the sushi counter at Sydney's Sokyo, to claim one is to trade in so-so for something better. And should you get chef Uein Hayashi Lee (formerly at Koko and before that, fresh from Kyoto) at your service, there is a lot to recommend about the Akaiito robata grill experience.

It begins with appetisers, prettily laid out: a Moonlight oyster sparkling with tart-sharp tomato vinaigrette and finger lime; robata-warmed octopus, cut to tender rounds in a salad with pickled onion, fennel and more fresh tomatoes. Wagyu tartare wearing a pickled shiitake hat with a rich nub of cured egg yolk teasing the line between luxe and fresh.

Next comes sashimi, whose hint at a higher level of care isn't just from the meticulously pristine box from which it's drawn. Nor the freshness, though the creaminess of New Zealand scampi, the sweetness of a scallop brought in from Japan or the light curing of the snapper tells that story. Instead, it's the light, floral, not-too-salty soy sauce Lee makes in-house, from scratch, for the course.

This is, unquestionably, a good time for fish fans. Nimble knife work and glitz follows – kingfish belly is simply scored with a million paper-fine cuts so a flash flaming catches the edges to caramelise its fats. Salmon, finished with an olive oil and truffle notch, is a fruity, floral surprise. Otoro, the rich tuna belly mic drop, is crowned with sterling caviar.

And there's still quality robata moments to come. Ox tongue, a touch chewy, is scorched and seasoned in all the right places. Tsukune, all fluffy, ginger-and-shallot-flecked chicken farce, is one of the lightest, most elegant versions in town. A juicy, crisp-skinned lobe of sea perch has only sea salt, grated radish and soy for company. And that is all it needs.

If only the take home message was: "this is a great omakase restaurant". But this is a great omakase experience trapped inside a restaurant mired in troubles. Service up top is enthusiastic, but unpolished. Being told multiple wines and beers aren't available is the extent of drink advice, though you do get your choice of sake cup from a pretty wooden box. Diners at tables look impressively unimpressed. No wonder, when an a la carte bill can easily hit $80 a head.

Comparatively, $115, which includes two final courses of braised green lip abalone in a dashi-cream sauce and slow-cooked short rib from the kitchen (admittedly the weaker dishes, both being a little wan and bizarrely preceded with a dessert-sweet palate cleanser of raspberry sorbet), is the better deal, and neatly dodges dodgy service for that of a chef.

As a package Akaiito is a troubled one, and I've had to score it thus. But food fossickers are never afraid to dig for their diamond in the rough.

Vegetarian With notice.

Drinks An OK list of Australian wine beers and Japanese sakes – when available.

Cost $115 for roughly 13 dishes.