Japan's Rugby World Cup heroes on Wednesday vowed to go for broke in their historic quarterfinal against South Africa on Sunday, insisting the Brave Blossoms have "nothing to lose" after reaching the knockout round for the first time.

"The goal for the Japan team was to get to the quarterfinals, and we have achieved that now," said fullback Ryohei Yamanaka. "None of the players have any experience of playing in a World Cup quarterfinal so we have nothing to lose. We just need to see how far the rugby we've been playing can take us.

"We need to keep doing the things we have been doing. We don't need to do anything differently just because we're playing South Africa. We just need to prepare as we always do, and make sure we do it properly over the whole week."

Japan is preparing to play South Africa at Tokyo Stadium having finished top of Pool A with four wins out of four, beating Tier One sides Ireland and Scotland as well as Russia and Samoa, and taking bonus points from three of those four games.

Japan has stunned the world and captivated the nation with its achievements at the first Rugby World Cup ever to be held in Asia, with a live domestic TV audience of 50 million expected to be announced for NHK's broadcast of the Brave Blossoms' 28-21 win over Scotland in Yokohama last Sunday.

That figure came in addition to the 67,666 fans inside International Stadium Yokohama, and Japan loose forward Uwe Helu said Wednesday that the atmosphere they created will live with him forever.

"I'm still getting the winning feeling from the last game," said Helu. "Just finding out how many people were watching the game. We always knew that if we kept winning, lots of people would support us. It's a good feeling. Just the energy. I think they just give us more energy.

"For me, we already met our goal. No one expected us to make the top eight but we proved everyone wrong. No one thinks we will win this game this week, so it's another chance to prove people wrong. We will give everything for our fans, knowing that they will always support us. When you win something, you just want to keep going."

Japan standoff Yu Tamura finished the pool stage as the competition's top points scorer on 48 points, while winger Kotaro Matsushima shares the lead in the try-scoring table on five with Wales' Josh Adams.

As a team, Japan picked up no yellow or red cards throughout the pool stage, and hooker Atsushi Sakate believes the Brave Blossoms are reaping the benefits of head coach Jamie Joseph's no-nonsense approach.

"We've been very strictly coached in training," he said. "We've been taught to be very smart in defense so that we don't pick up yellow cards. Our reactions and decisions are very strictly supervised in training, and I think that shows in our games.

"It's a great atmosphere in the team. We've been working over the past four years to improve ourselves, and the fact that we've been able to grasp that gives us a lot of confidence and makes us happy.

"But we're thinking about what comes next now, and we're getting ready for the next game. We won't change anything over this week but we will have more confidence than before."

Helu also paid tribute to Joseph's guidance, describing the 49-year-old New Zealander as a "mental coach" who has given the players more belief.

"I think he's a really honest person," said Helu. "What he wants you to work on, he'll come straight to you and have a one-on-one meeting and tell you, 'you need to do this and you need to do that.'

"That's the good thing about him. I like coaches who are honest like that. It keeps everyone on their toes and makes sure they do their own job, to focus on what they have to do in a game."