Increased character rank
Every time the game is finished in story mode, the rank of the extra characters in versus and survival modes will be raised. This does not include Volt, Sion, and Kou.

Dauragon fighting with one arm
Play the game in story mode and beat Dauragon at his first encounter. The one armed fighting version of Dauragon will be accessed in versus and survival modes.

Dominique
Play the game in story mode until Dominique demolishes the group of PD-4s to access her in versus and survival modes.

Kaldea
Beat Kaldea before the last encounter with Dauragon in story mode to access her in versus and survival modes.

Echidna
Finish the MSD Cargo Train level to unlock Echidna.

Leann Caldwell
Play through the game entirely, only selecting Kou. After you beat Dauragon for the last time you will see a FMV sequence where you have to battle Leann. Beat her to unlock her in versus mode.

Kou with MSF costume
Play through the game entirely, only selecting Kou. Save the game after Kou enters the Mikado building as a MSF soldier. The MSF costume for Kou will now be unlocked in survival and versus modes.

PD-4
Beat the PD-4 during story mode to access it in versus and survival modes.

Hidden FMV sequence
Finish the game as Sion.

Bonus characters
Finish the game to unlock bonus characters each time that it is completed. Additional finish the game (not in story mode) once to unlock Echidna, Dauragon1, Dauragon2, Dauragon3, Mogetsu, Mogetsu unmasked, PD-4, Dominique, and Kaldea.

Sion with black hood
Finish survival mode by beating the black-hooded version of Sion to unlock this costume in versus and survival modes.

Wong Leung
Use only Volt or Kou through the game. However, when you are going to battle Threw for the final time, select Sion. When you complete the game, Sion will have a flashback. Beat Wong Leung to unlock him in versus mode.

Dauragon topless
Finish the game for a third time using any character. After beating Dauragon for the second time, he will get up again and fight topless. Beat him to unlock him in versus mode.

Mugetsu with mask
Finish the Mikado Building-Hanging Garden level to unlock Mugetsu with his mask.

Mugetsu without mask
Finish the Galeos-Mid Flight level to unlock Mugetsu without his mask.

Hints & Tips

Team sacrifices
Do not worry if any of your CPU controlled partners gets beaten. As long as you are still standing, they will return for the next battle.

Easy experience
During in any battle, look at the top right of your screen. When one of the bubbles that represents an enemy is colored red, go to that person and rapidly kill them. You will get the experience while your partner(s) did all the work.

Bar Fate battle
The first battle is in Bar Fate, with MSF Agents as your foes. This is your initial fight. Get used to the play mechanics and earn yourself some experience. It does not really matter if you win this fight or not it is one of a few that you can actually lose without the game being over. Get a feel for what chains work best for the Bouncer you have selected.

Kou: Phone conversation
Take Kou on the first battle against MSFs at Fate. When Kou calls Leann, you will hear what she says to Kou.

Beating Dauragon

Sion: Use Sion's last attack, the Hurricane Blitz. First, let Dauragon hit another party member. When he is busy, use Hurricane Blitz. When he gets up, do it again. Keep repeating this until you destroy him. Note: No one can cover from that attack, not even Dauragon.

Sion: Obtain Sion's Double-Knuckle attack. At first, back away from the party and block (R1). Then, get behind Dauragon. You should be able to get off three hits with the move, taking away a lot of health. It is possible to fight through all three Dauragon modes and beat him overall with over half your health left over.

Sion: Battle Dauragon, and knock him down in some way. Every time he gets up, constantly use Sion's Floating Mine attack until he is beaten.

Volt: Use Volt's Lift Up Slam attack. Let your party divert Dauragon, then use the Lift Up Slam attack. When he is getting up, use it repeatedly until he is beaten. Do not use against a wall or it will not work give him some space if he is against the wall.

Kou: Use Kou's Tiger Frenzy attack. Use this attack non-stop, so that Dauragon's  chance of attacking or covering is next to zero. Note: When he falls, use it the instant that he gets up.

Beating most Bosses easier
Play as Kou. After you have gotten his uppercut attack, wail. If you timed properly, you can "juggle" the enemy in the air many times.

Team attack
Immediately press R2 whenever you hear one of your teammates make a taunt. Most of the time everyone will all team up against an enemy. This move will mostly always be blocked by the final Boss.

Fight Dauragon only twice in the last battle
Play as Sion throughout the game. Dauragon will only battle you twice instead of getting up topless.

Kaldea: Three deaths

Do not use Sion when you get separated or in the ship where you see the panther.

Do not use Sion when you get separated, but when you see the panther in the ship use Sion.

Use Sion when you get separated and in the ship when you fight the panther.

Sion: Three final stories

Song's story: Play with Kou or Volt through the game. However, use Sion when you are going to fight against Dauragon. Sion will think about his master.

Kaldea's story: Do not use Sion when you get separated. Use Sion in the ship when you see the panther and in the final battle. Sion will remember what Kaldea said.

Dominique's story: Use Sion when you get separated, when you see the panther in the ship, and when battling Dauragon to see Dominique's story.

Card key
When in the scene where you have to acquire the card key, go down so that you are in the second screen. You should see a small yellow lunch box in the bottom left corner. If done properly, and not accidentally, go into the first screen to get the Card Key and not have to run from the doors.

Differing from other information, to get the card key open all three boxes. There is one lunch box on either side on the seats. Just walk up to it to open it and move on swiftly to the next one. The third box in a briefcase in the back of the train, the key will be inside.