With Japan's opening game at Rugby World Cup 2015 less than four days away, the Brave Blossoms are slowly starting to realize the enormity of the tournament.

"I'm not in my usual state of mind, that's for sure. This is my first World Cup after all, and I'm looking forward to it," Toshiaki Hirose said Tuesday in Brighton, where Japan takes on South Africa on Saturday.

Fellow back Harumichi Tatekawa feels the same way about a tournament that has broken all previous tickets sales records.

"To be perfectly honest, there's a part of me that's having a blast and a part of me that's nervous because I'll be playing under the kind of pressure I've never experienced. But all in all, it's good. I'm spending each and every day feeling really sharp."

Japan names its team for Saturday's game — its first ever test match against the Springboks — on Thursday afternoon, and Hirose was under no illusions as to what the Brave Blossoms need to do if they are to produce the biggest upset the tournament has ever seen.

"The most important thing will be whether we can believe in ourselves enough," he said. "We're obviously going to analyze them to the smallest details but we have to be able to believe in what we're doing. That's what it will come down to."

However, as assistant coach Steve Borthwick pointed out, the Springboks — who won the 2007 World Cup with current Japan coach Eddie Jones as technical director — will also have done analysis of their own.

"Clearly, Eddie does know a lot about South Africa and South African players, but the level of analysis that will be done by every team at the World Cup — particularly teams like South Africa — will be extraordinary.

"So they will have researched every one of our players and watched every one of our games over the last few years. They will have looked at the players in the Top League and every game they played for Japan. I think they'll know a lot about us as well."

Former Australia rugby league international Craig Wing knows a thing or two about big games but admitted representing Japan at the World Cup, which was recently declared the most expensive sporting event ever, was taking things to a different level.

"Opening game for the World Cup, it doesn't get better than that. We feel that we've gone up a level and everyone feels a little sharper and excited."

And did he think Japan could upset the form book?

"They play their style of football, we play ours. We've been preparing for quite a long time and most of the focus has been on this game.

"Everyone writes us off, wants us to just fly the flag, but we've all sacrificed a lot of time, particularly away from our friends, our families, our lives. We're not here to make up the numbers, we want to make a difference."