Unlockable Characters
Unlockable How to Unlock
Ein Beat Story mode with Hitomi
Gen Fu Beat Story mode with Eliot
Leon Beat Story mode with Zack
Helena Beat Story mode with all 16 characters
Nicole (Spartan) Beat Story mode with Helena
Tengu Beat Time attack for all characters, including unlockables

Unlockable Costumes
To get a costume for character that can be used in the story mode(16 default + Helena), beat storymode with that character once for a costume. For character that can't be used in story mode, simply beat Time Attack mode [with default settings] instead. Difficulty doesn't matter.
Unlockable How to Unlock
Kasumi C3-C7 Beat Story mode with her one time per costume.
Kokoro C3-C7 Beat Story mode with her one time per costume.
Hitomi C3-C8 Beat Story mode with her one time per costume.
Helena C3-C5 Beat Story mode with her one time per costume.
Leifang C3-C7 Beat Story mode with her one time per costume.
Tina C3-C5 Beat Story mode with her one time per costume.
La Mariposa C3-C5 Beat Story mode with her one time per costume.
Ayane C3-C6 Beat Story mode with her one time per costume.
Christie C3-C4 Beat Story mode with her one time per costume.
Spartan-458 C3-C7 Beat Time Attack mode with her one time per costume.
Hayabusa C3-C4 Beat Story mode with him one time per costume.
Elliot C3-C4 Beat Story mode with him one time per costume.
Brad Wong C3 Beat Story mode with him one time per costume.
Bayman C3 Beat Story mode with him one time per costume.
Bass C3-C4 Beat Story mode with him one time per costume.
Zack C3-C4 Beat Story mode with him one time per costume.
Jann Lee C3-C4 Beat Story mode with him one time per costume.
Hayate C3-C4 Beat Story mode with him one time per costume.
Ein C3-C4 Beat Time Attack mode with him one time per costume.
Genfu C3-C4 Beat Time Attack mode with him one time per costume.
Leon C3-C4 Beat Time Attack mode with him one time per costume.

System Voices
Each character has his/her own voice for the system. To unlock the particular characters system voice, you must complete their excercise in sparring mode.
Hidden Stage
Sparring stage, floor mat with no walls.

Unlockable How to Unlock
Nassau Station Becomes available once Nicole (Spartan-458) is unlocked

Theater Mode
Complete "Story Mode" once using any character to unlock "Theater Mode". The movies for each characters will be unlock once you finish their story.

Unlock Tatami Stage
Get all costumes and complete each character's exercise (including unlockables) to get access to the Tatami stage for use outside of Sparring mode.
Unlockable How to Unlock
Tatami Stage Get all costumes and complete all Exercises (including Unlockables)

All secret achievements.
This is a list of all 15 secret achievements and how to unluck them in Dead or Alive 4.
Unlockable How to Unlock
0 Gamerscore Points Lose 5 online matches in a row.
0 Gamerscore Points Lose 10 online matches in a row.
0 Gamerscore Points Lost 20 online matches in a row.
0 Gamerscore Points Achieve a grade "D" in DoA4 online.
0 Gamerscore Points Achieve a grade "E" in DoA4 online.
Achieve a Bronze Star. 10 Gamerscore Points. Beat someone with a 10-14 win streak in DoA4 online.
Achieve a Silver Star. 20 Gamerscore Points. Beat someone with a 15-19 win streak in DoA4 online.
Achieve a Gold Star. 30 Gamerscore Points. Beat someone with a 20+ win streak in DoA4 online.
Unlock Leon. 10 Gamerscore Points. Complete story mode with Zack.
Unlock Gen Fu. 10 Gamerscore Points. Complete story mode with Eliot.
Unlock Ein. 10 Gamerscore Points. Complete story mode with Hitomi.
Unlock Helena. 20 Gamerscore Points. Complete story mode with everyone.
Unlock Spartan-458. 20 Gamerscore Points. Complete story mode with Helena.
Unlock Tengu. 20 Gamerscore Points. Complete Time-attack mode with everyone. That includes secret characters.
Play DOA4 for 5 hours 5 Hours Played (10 Points)
Play DOA4 for 10 hours 10 Hours Played (20 Points)
Play DOA4 for 100 hours 100 Hours Played (40 Points)