Dead or Alive 4 - Hidden characters

Alternate character appearance:
At the character selection screen, press A to select a character, then press X, Y, or Start. Press A to start the match with the alternate appearance. Not all characters have an alternate version.

Alternate costumes:
Complete Story mode to unlock an alternate costume with the following characters. If available, the next alternate costume for that character will be unlocked when Story mode is completed with them again.

Ayane C3, C4, C5, C6
Bass C3, C4
Bayman C3
Brad Wong C3
Christie C3, C4
Elliot C3, C4
Hayabusa C3, C4
Hayate C3, C4
Helena C3, C4 C5
Hitomi C3, C4, C5, C6, C7, C8
Jann Lee C3, C4
Kasumi C3, C4, C5, C6, C7
Kokoro C3, C4, C5, C6, C7
La Mariposa C3, C4, C5
Leifang C3, C4, C5, C6, C7
Tina C3, C4, C5
Zack C3, C4

Complete Time Attack mode on the default settings to unlock an alternate costume with the following characters. If available, the next alternate costume for that character will be unlocked when Time Attack mode is completed with them again.

Ein C3, C4
Genfu C3, C4
Leon C3, C4
Spartan-458 C3, C4, C5, C6, C7

Biolab Core stage:
Complete Story mode.

Bonus system announcer voices:
In the options menu, you can choose different voices for the system announcer. To unlock additional voices, enter Sparring mode and bring up the sparring menu. Select Exercise and you will be prompted to run through an extensive moves list. Complete the moves list to unlock that character's voice as a system announcer. Complete Exercise mode with all default and bonus characters to unlock Alpha-152's system voice.

Easy wins with Jann Lee:
Try to land a critical punch or kick to the enemy's head. If not accomplished, make use of quick countering or blocking to land a firm blow. Then when your enemy is hit off balance for a few seconds, keep throwing random critical blows to the head region mainly, and mix it up slightly to the body and legs. If you can do this and include fast combos in between your rhythm, you should be able to keep the enemy off the ground desperate for making successful blows. You should be able to do this technique with simple combos. Make sure that your rhythm is broken, meaning attack at different times without staying in a similar pattern and keeping your blows mostly critical. If you can do this a lot, you should also be able to switch it up with fast combos making it almost impossible for your opponent to counter. Remember to execute critical blows to the head mainly, mixed with fast combos and quick blows to the body. Keep your rhythm broken so it is impossible to counter no repetition or repeating the speed of blows, and make sure to keep your guard up. Do not allow the enemy to hit you unexpectedly, or they may confuse you with the same trick. Try to at least counter when you lose balance in the match.

Gamerscore points
Accomplish the indicated task to get the corresponding number of Gamerscore points:

Achieve a Bronze Star 10 points: Defeat someone with a 10-14 win streak in Dead Or Alive 4 Online.
Achieve a Gold Star 30 points: Defeat someone with a 20 win streak in Dead Or Alive 4 Online.
Achieve a Silver Star 20 points: Defeat someone with a 15-19 win streak in Dead Or Alive 4 Online.
Unlock Ein 10 points: Complete Story mode with Hitomi.
Unlock Gen Fu 10 points: Complete Story mode with Eliot.
Unlock Helena 20 points: Complete Story mode with all characters.
Unlock Leon 10 points: Complete Story mode with Zack.
Unlock Spartan-458 20 points: Complete Story mode with Helena.
Unlock Tengu 20 points: Complete Time Attack mode with all default and hidden characters.

The following are secret achievements, but will earn no Gamerscore points:

Get a D rank in Dead Or Alive 4 Online.
Get an E rank in Dead Or Alive 4 Online.
Get an F rank in Dead Or Alive 4 Online.
Lose 5 consecutive online matches.
Lose 10 consecutive online matches.
Lost 20 consecutive online matches.

Halo reference in the game:
Select Spartan-458 and play on the Gambler's Paradise stage. During the match, a Warthog with Marines will appear on the road.

Hidden goof rewards:
Some of the game's secrets shown in the achievements list are actually goof rewards. These vary from Loss Streaks to Rank Demoting.

Increased bounciness:
Enter 99 as your age in your profile to make the female characters breasts bounce nicely.

Nassau Station stage:
Complete Story mode with Helena.

Play as Ein:
Complete Story mode with Hitomi.

Play as Gen Fu:
Complete Story mode with Eliot.

Play as Leon:
Complete Story mode with Zack.

Play as Spartan-458:
Complete Story mode with Helena.

Play as Tengu:
Complete Time Attack mode with all default and hidden characters.

Tatami Mat stage:
Unlock all costumes and system voices and Complete Story mode with all seventeen characters.

Theater mode:
Complete Story mode with any character.