Jamie Joseph said Thursday his main motivation for leaving Super Rugby champions the Highlanders to become head coach of the Brave Blossoms was the chance to lead Japan when it hosts the 2019 World Cup.

"It's really hard to leave but I want to improve as a coach," the former All Black and Brave Blossom said at a news conference in Dunedin, New Zealand, audio of which was provided to Kyodo News.

And "the big incentive" was Rugby World Cup 2019 and a chance "to renew my close relationship with Japanese rugby."

"They are the hosts of the World Cup in 2019 and to be involved in the team and host nation is probably the biggest carrot," Joseph said.

Joseph, who played 20 tests for the All Blacks between 1992-1995 and nine for Japan, representing the country at the 1999 World Cup, will take charge of Japan at the completion of the Super Rugby season.

The former Sanix Blues forward replaces Eddie Jones, who announced his decision to leave Japan in August before leading the team to its historic three wins at last year's Rugby World Cup. Jones has since gone on to become England coach.

"I lived in Japan for eight years and have been going back and forth over the years, keeping in touch with friends," said Joseph. "So it's not a difficult transition or the normal transition for a foreign coach. So it was easier to make the move."

The 46-year-old Joseph said he was approached by the Japan Rugby Football Union prior to Christmas and that he has signed a deal to take him through to the end of the 2019 World Cup.

"I wouldn't have gone if that was not the case," he said. "The Highlanders were very keen to keep me here and it was a really tough decision to say no to that."

However, he will not leave for Japan until August so the Brave Blossoms will need an interim coach to lead them when they take on Scotland on June 18 and 25.

"I am contracted to the Highlanders," he said. "It (the Scotland tests) was obviously a talking point with the Japanese rugby union. My answer to that is that I am committed right to the end with the Highlanders so I didn't want and couldn't be involved with it (the games against Scotland).

"If I was going to do it justice and show the integrity that I am passionate about with the Highlanders then I couldn't be involved with another team. So that's the way it is."

Joseph said at this stage he was not thinking of taking his assistants — former Panasonic Wild Knights flyhalf Tony Brown and former Toshiba Brave Lupus center Scott McLeod — with him to Japan.

"They (the JRFU) really (just) wanted a head coach," he said.

He also suggested the Brave Blossoms and Japan's new Super Rugby side, the Sunwolves, would be closely linked.

"They've got themselves in a situation where they are now in the Super Rugby competition. They found it hard to find coaches to coach the Sunwolves, but they've found three ex-All Blacks now," he said.

"(Sunwolves forwards coach) Filo (Tiatia) has had experience in Japan and played and lived up there, so he'll know a fair bit about it, and (head coach) Mark Hammett is obviously an experienced coach at that level so that's a step in the right direction for Japan."

Joseph admitted that while he still harbored thoughts of one day coaching the All Blacks, "you have to be worthy to coach the best team in the world."

The Japan job he said was "another step towards that and another opportunity and chance for me."