The former England rugby captain Steve Borthwick will take up a coaching role with Japan after hanging up his playing boots with Saracens next weekend.
The lock-forward will become Japan's forwards coach, as the Cherry Blossoms prepare for next year's World Cup in England.
Japan on Sunday qualified for the 2015 rugby World Cup by thrashing Hong Kong 49-8 in Tokyo.
The victory handed them a seventh Asian Five Nations title.
Japan will have appeared in every World Cup to date and they will join South Africa, Samoa, Scotland and the United States in Pool B of the 20-team tournament.
The move means Borthwick, who has helped the Japanese in the last two years in an ad-hoc capacity, will formally link up with former Saracens director of rugby Eddie Jones.
Former Australia coach Jones has been Japan's head coach since 2012.
Japan say they will look to Borthwick to hone their lineout skills.