Two years ago, Heihachi failed to capture Ogre. Not willing to give up, Heihachi ordered his researchers to collect blood samples, skin tissue and hoof fragments left behind by Ogre (or known as True Ogre in its true manifestation) in order to conduct genetic experiments. Heihachi's goal was to create a new life form by splicing Ogre's genome with his own. However, the research was unsuccessful.

After extensive experimentation, Heihachi's bioengineers came to the conclusion that an additional gene - the Devil Gene - was necessary in order to successfully splice Ogre's genetic code into another living organism. Heihachi learned that his own genome lacked the Devil Gene, but he knew someone who did…

Secrets

Attack All Enemies (Tekken Force Mode)
When using a move combination with King in Tekken Force mode, it will damage all enemies standing close to you as well. Though it makes fights easy, it tends to eat up valuable time.

Display Attack Names during game.
In Arcade/Time Attack/Team Battle/VS mode, press Select during the game and you will see the names of your attack moves. Every time you enter a command attack, its Japanese name will be displayed.

Practice Mode Move Percentage
Enter Practice mode and select any character. Then press start and choose the command list. Now press and hold any of the shoulder buttons (R1,R2,L1,L2) and you should see the percentage of how many times you have performed that move in practice mode instead of the button combination for the move.

Glitches

Play the Arena stage without any cages. (JP Version Only)
This is a glitch more than a Code, but you can use it to play in the Arena stage without any cages.

1) Finish Time Attack Mode.

2) Play Story Mode using the SAME CHARACTER. When you reach the final stage, skip Heihachi's intro (ie. press Start).

When the round begins, you'll see that the cages are down (actually, they're invisible). You can leave the Arena by going to the ramp which Heihachi walked down in the intro.

Note: In order for this code to work, you must play as a character who actually fights in the Arena Stage during story mode (for instance, Jin never fights in the Arena, so the glitch doesn't work for him).

Here's the hard difficulty Tekken 4 playthrough: