Bartender Akihiro Sakoh recalls clearly when Japan’s most popular cocktail hack took off. It was the 1990s and he was working in a hallowed Tokyo drinking institution called Gaslight under the tutelage of Takao Mori, an elder statesman of Japanese bartending.

“People would order a Gin & Tonic and they were always surprised,” Sakoh says. “Other bartenders would come in and try to figure out what was different about Mori-san’s version, why it wasn’t so sweet. Like: Maybe he’s adding salt?”

But they were wrong. The actual secret ingredient? Soda water.

It was an idea born of necessity. Until the mid-1990s, the Japanese government banned quinine, tonic water’s defining ingredient, from food or drink. Consequently, tonic waters in Japan were (and still mostly are) little more than fizzy, sweetened water. Pour a few ounces of that on a gin and you douse all of the spirit’s details.

When Mori added soda water to the tonic, he lightened the palate, allowing the gin to shine, then added two bar spoons of lime juice to give the drink balance. “It’s delicious,” says Mori, who now runs two eponymous bars in Tokyo’s ritzy Ginza district. “But it wasn’t my idea. I don’t know where it came from.” 

Nobody does. Some, like Takuo Miyanohara of Bar Orchard, also in Ginza, believe it was inspired by a whiskey drink called the Presbyterian, which also mixes two sparkling toppers: ginger ale and soda.

Tamiko Matsuo, who also trained with Mori and now owns Ginza’s Bar Landscape, suggests the citrus situation had something to do with it; limes used to be prohibitively expensive in Japan. “Only hotel bars could add wedges to a drink. Regular bars could only afford bottled juice,” she says. “So people got used to the idea that a Gin & Tonic was a sweet drink, but if they asked for something refreshing, the bartender would use soda.”

The man who has done the most to popularize the recipe is Seiji Oshiro, who opened Hibiya Bar in 1990 in Tokyo with a mission to make cocktail culture accessible to all. It was a roaring success and grew into a chain of 30 bars. In 1997, he added the soda-topped G&T to his menu under the name by which it is still known: the Gin Sonic.

Japan’s Gin & Tonics were too sweet, he reasoned, and Gin Rickeys too tart for neophyte drinkers. The Sonic, a portmanteau of soda and tonic, was the Goldilocks drink. In 2003, Oshiro pushed things even further when he opened the whisky-themed Hibiya Bar Ginza-S and created the Whisky Sonic. It became such a success that Suntory now produces a bespoke blended whisky for the bar, intended to suit the Sonic style. The whisky tastes almost brittle when drunk straight, but comes to life when topped with tonic and soda. 

The Sonic theme is everywhere in Tokyo now. There’s the Absinthe Sonic at Bar Trench, Mezcal Sonics that are top of the menu at premium spirit tasting bar Mangosteen, and, if you order a G&T, Moscow Mule or Cuba Libre at Bar BenFiddich, each will come with the mixer cut with soda water. 

Japan’s government has relaxed the rules on quinine, slightly, and though none of the local producers have been persuaded to add the bitter bark to their recipes, imported tonics do contain at least the essence of it. For some bartenders, that’s reason enough to ditch the Sonic style. For others, though, soda still makes sense.

“The function of ‘Sonic’ has changed,” says Yasuhiro Kawakubo, who runs Bulgari Ginza Bar. “Now we have more tonics, but we have new craft gins too. If you want to showcase the real taste of these gins, Sonic style is best.” To best highlight the spirits, he says, use even more soda, compared to tonic: Kawakubo suggests 70 milliliters (about 2 1/2 ounces) of soda to 20 milliliters (a heavy half-ounce pour) of tonic on a 30-milliliter pour (about 1 ounce) of gin.

Meanwhile, at Akihiro Sakoh’s Sakoh Bar, you can order a Gin Sonic and he will serve it with three parts gin to two parts tonic and one part soda, with a squeeze of lime. You can also order a Gin & Tonic, and you’ll get exactly the same drink—because if it works, it works.