Japan will be coached by Tony Brown for Saturday's game against Tonga after head coach Jamie Joseph returned to New Zealand earlier in the day following the death of his mother.
The national team performance committee vice chairman Yuichiro Fujii called a media briefing 90 minutes before the game at Hanazono Rugby Stadium in Higashiosaka to say Joseph had left the team hotel earlier in the day.
"Jamie's mother passed away last night at around 9:30 p.m. Japan time and Jamie found out in the middle of the night," Fujii said.
"She had been ill for a while but her condition worsened before (last week's) Kamaishi match (against Fiji) but Jamie wanted to stay with the team."
When the news broke of Maude Joseph's death, team captain Michael Leitch and other senior players told Joseph he should return home.
Fujii said Brown would act as head coach on Saturday with Shin Hasegawa in charge of the forwards.
"The team have promised to play for him," Fujii said of Joseph, whose mother was 78, adding that he was expected to rejoin the team next week in Fiji when they take on the United States.