Tokyo - Michael Leitch is Japan's poster boy, but like many other players at the Rugby World Cup he's not representing his country of birth - he's a product of New Zealand's seemingly endless production line of talent.

A country which has won three of the eight World Cups so far, and is among the favourites to add a fourth in Japan, puts rugby brawn and brains alongside dairy products and meat as a leading export.

It has almost become a must-have accessory to have a New Zealand connection at the World Cup, where more than a third of the head coaches and 12.5 percent of the players are from the rugby-obsessed land at the bottom of the world.

For New Zealanders, it's the game itself and not just the world-champion All Blacks that captures the imagination, and players and coaches who can't crack the top team see joining cash-rich clubs abroad as the next best thing.

Nick Evans, who played 206 games for the London Harlequins after 16 Tests for the All Blacks, says he "probably wouldn't have gone overseas" if he hadn't found his way to New Zealand's 10 jersey barred by the great Dan Carter.

Willie Heinz was so far down the New Zealand scrumhalf pecking order that he went to Gloucester in 2015 to get a break, and is now playing for England.

Other players like Leitch - who, in a country where rugby is a fringe sport, recently finished second to Prime Minister Shinzo Abe in a poll of Japan's most recognised public figures - left New Zealand at a young age for education reasons, or when their parents moved.

Chris Boyd, who took the Hurricanes to the 2016 Super Rugby crown, said he had no choice but to take up a role as director of rugby at Northampton last year.

"Once you get to Super Rugby head coach in New Zealand, there's really nowhere to go and I think it's an issue potentially for New Zealand Rugby that there's a lot of experience and intellectual property that ends up going overseas," Boyd said on his departure.

But New Zealand rugby boss Steve Tew does not believe it is a problem.

Tew's philosophy runs counter to the norm that the ingredients for success must be a closely guarded secret, and under his watch New Zealand has been only too willing to share coaches and training tips.

"If you don't have good coaching then you won't have a successful sport, not long term," Tew said.

"You might get away with it in the short term, but for long-term, sustained success you need a very good development programme and coaches, which we produce on a regular basis."

With 26 teams in domestic competitions feeding five Super Rugby clubs, which in turn stock the All Blacks, the internal pathway is narrow.

Like Boyd, Graham Henry and Steve Hansen used coaching success at club level to sign top European contracts, which became a springboard for taking charge of the All Blacks and winning the World Cup - Henry in 2011, and Hansen in 2015.

Current Wales coach Warren Gatland, another New Zealander, is returning home to join the Waikato Chiefs franchise after this World Cup and is tipped to take the reins of the All Blacks in future.

Along with New Zealand and Wales, Ireland (Joe Schmidt), Fiji (John McKee), Samoa (Steve Jackson), Georgia (Milton Haig) and Japan (Jamie Joseph) all have New Zealanders at the helm.

Hansen believes harnessing coaching talent should be the focus for emerging rugby nations.

"It's not a coincidence that a lot of the coaches around the world at the moment are New Zealanders and it's no coincidence that we have a lot of talent back in New Zealand because the systems those coaches are coming out of are producing a lot of players," he said.

"We don't have a lot of money so I don't think money is just the answer. It's about rugby education, some natural talent through our bloodlines."

By the numbers, 27 of the 31 All Blacks are New Zealand-born as are 50 players scattered across 11 other teams.

Excluding New Zealand, eight of the top 10 ranked countries have New Zealand-origin players including Japan (five), Australia and Scotland (three), England and Ireland (two), and Wales and France (one).