Jaycee is an alter-ego for Julia Chang to make her appearance in Tekken Tag Tournament 2. She was at first unnamed, but was later given the name Jaycee. She is a luchador, but her fighting style has not yet been revealed. Although, it has been shown she has some old moves she had as Julia, as well as some new ones.
It was originally rumored that she might be an alter-ego for Julia Chang, due similar body build, similar pendant to the one Julia wears and the fact that J.C. is pronounced the same as Jaycee and also stands for Julia Chang. She was later seen in a new gameplay video with Julia's moves and voice and Julia herself was not seen in the select screen, confirming that she is in fact Julia. Jaycee's name will automatically change back to Julia, depending on what customizations you give her.
Julia has decided to adapt to the name Jaycee and the luchadore outfit in honor of her injured luchadore friend.