Here is how do you select him first highlight heihachi on the character select now you're going to do the hidden command press down up hold up start start release up up and if you did that correctly the cursor will disappear and Kazuya will be highlighted and selected
I know this comment is two years old so you probably have already figured it out by now or not. Whatever the case is, here is how you unlock Kazuya. You just got to beat the game with all base characters. Jun, Yoshimitsu, Nina, Law, Heihachi, Paul, King, Michelle, and Lei. After that you will unlock the sub-boss characters for each character respectively. Lastly, you just have to beat the game with any sub-boss, and there you go. Kazuya is all yours.