The hosts have named Asaeli Valu, Uve Helu, Amanaki Lelei Mafi, William Tupou, Ataata Moeakiola, Lemeki Romano and Nakajima Isileli.
Mafi received minor injuries in their warm up match against South Africa but was given the green light for the RWC.
The powerful No.8 and and flying wing Kenki Fukuoka were both forced from the field, leaving head coach Joseph with some headaches ahead of his side's Pool A opener against Russia in Tokyo on Sept. 20.
Fukuoka pulled up lame away from the ball in just the fourth minute and was seen on crutches later on, while Mafi looked to be holding his right shoulder as he left the field early in the second half.
Mafi is one of the more than 20 percent of players that are of Pacific Island descent at the tournament.
Japan will be playing against Russia in this year’s World Cup opener on Friday.