TOKYO (AFP) - For all the talk of samurai spirit, Japan have revealed an unusual recipe for their World Cup success - a rice dish with pollock roe and whitebait rustled up from leftovers.

Hooker Takuya Kitade has yet to make a tournament appearance for the Brave Blossoms, who have stormed into the quarter-finals for the first time ever, but he is the culinary wizard behind the fishy treat the players are tucking into between games.

While Japan captain Michael Leitch has spoken of the "dark side" of Japan's game - part of the mental and tactical toughness underpinning their fairytale run - Kitade sounded more Gordon Ramsay than Darth Vader.

Japan's secret weapon is certainly not for the squeamish, containing fully ripe eggs taken from fish ovaries.

"The players call it the Kitade Bowl," the Sunwolves hooker explained as the Japanese prepare to face South Africa this weekend, when they will try to repeat their "Brighton Miracle" at the 2015 World Cup.

"It's basically just a little dish I threw together using whatever ingredients I could find in the kitchen - leaf mustard, pollock roe, whitebait and onions with an egg cracked on top. For a sauce, I drizzle a bit of sesame oil over it."

Kitade described how the rest of the Japan team had looked on in astonishment as he created his protein-rich snack.

"I was just feeling a bit peckish after the Samoa game so threw it all in the mix," he added.

"The other players were all asking 'what on earth is that?' - but 70 per cent of them are eating it now!"

Kitade was asked what Leitch had meant when he said Japan were learning to use the dark side during their Pool A wins over Russia, Ireland, Samoa and Scotland.

"Leitch was referring to the darker side of human nature," he smiled.

"We've got to be prepared to tough it out with opponents and get a little nasty from time to time."

If Japan have discovered a mean streak, it is their togetherness and free-flowing rugby, rather than their deployment of the game's dark arts, which has earned the history-makers the biggest plaudits on their way to the last eight.

"We've achieved our target as one team," said replacement scrum-half Kaito Shigeno, warning the Springboks that their 41-7 thrashing of Japan in a World Cup warm-up last month would mean nothing in Tokyo on Sunday (Oct 20).

"South Africa took us out of our game plan last time. But if we stick to it, we can produce another shock."