He also had a run at number 12 against Bath. His defensive performances have been excellent, but he can also play with the ball. Thomas is missing because of a calf injury. Hawkins has been left out of the 23-strong squad for the autumn games. Llewellyn, 6ft 6in (1.96m) and 16st 12lbs (107kg), will wear the 12 jersey, with James, 6ft 4in (1.90m) and 16st 3lbs (103kg), outside him.
Nine of the 15 starters against Japan, including six of the eight forwards, play club rugby in England. Twelve of the 23-strong squad are based there.
Defence coach Tandy has dropped his usual preference for a more recognised ball-player at inside centre.
The pair will form one of Wales' biggest centre combinations.
Llewellyn has been selected there instead.
He has played inside centre regularly for Cardiff, and coaches said they were confident he could deliver what they wanted.