After retiring from his playing career in 1994, he became coach of the Toshiba Brave Lupus whom he led to three consecutive national titles from 1997 and 1999.
His success with Toshiba Brave Lupus led to him to be appointed as coach of the Japan national team in December 2000 after Seiji Hirao resigned.
[1] He led the side up to the 2003 Rugby World Cup, where Japan put up some credible performances against Scotland and France but ultimately finished the tournament winless.
This was Mukai's last season in charge as he handed over the reins to new coach Satoshi Yamaguchi and moved into a directors role at the club.
[3] During his time as a coach, Mukai was renowned for employing an attacking game plan.