Before you can perform a Unison Attack, Kratos will need to teach you how.
This will definitely happen (a little into the game), so don't worry. When
the time comes, you'll be introduced to the unison attack gauge. This will be
displayed above the character portraits during battle. The guage will fill up
slightly each time you hit the enemy. It will fill up faster if you perform a
lot of combos (Which is difficult to do early on, so don't be discouraged if
it seems like it takes forever for the bar to fill). The gauge carries over in
battles, so you can save the unison attack for when you really need it. A
unison attack can be performed by pressing R3 (V Key) when the guage is full
(It turns red).

When you press R3 (V Key), the party leader will flash and perform a simple
swipe. The unison attack will only start if this swipe hits an enemy (and
they don't block). As soon as this happens, you will have about 1 second to
input your first command and you'll get about an additional second after that
for the next command and so on. When the unison attack begins, a button
interface will appear on the right side of the screen. Each character
in the party is assigned a button. Pressing their button in conjuction with a
control stick or D-pad direction will have them perform the tech move assigned to that
button and stick combination. If you want to change the tech assignments, you
can do so in the U. Attack screen, either in the menu screen or in the battle
options screen. Each character can only attack once during a unison attack, but
they don't have to. Techs performed during a unison attack do not require mana.

Now for the fun part. Characters can perform additonal moves together if they
used certain techs during the unison attack. These moves are performed
immediately after the main unison attack. For example, if Lloyd used Sonic
Thrust and Kratos used Sonic Thrust during the unison attack, they will
perform a special move afterwards called Cross Thrust where they attack
together. I've compiled here a list of unison attacks.

Getting a hang of the unison attack system can be very difficult at first
since you'll rarely get a chance to use it at the beginning. Here are some
tips for first time users: don't use the control stick at first. Stick to
simple button presses. For example, if you want to perform the Pow Blade
move, set Tiger Blade as the first attack for Lloyd in the Tech menu and
Pow Hammer as the first attack for Colette. Then when you perform the unison
attack just press the their corresponding buttons quickly. For example, If Lloyd is party
leader, then his button will be B (Left Shift). If Colette is in the second position, her
button will be A (E Key). Position 3 is X (F Key) and Position 4 is Y (Left Control).

Once you get a hang of unison attacks and the combo system, you can try to
link a unison attack to a combo string.

Example:

Hit
Hit
Hit
Sonic Thrust
Psi Tempest
Hunting Beast
-Start Unison Attack-
Demonic Tiger Blade
Judgment
Cyclone
Ray
Prism Stars

Q: Can I perform more than one special Unison Attack move at a time?
A: Unfortunately no. If you do set up two or more possible unison attacks,
only one of them will be performed. (See next question)


Q: How do I know which one will execute then?
A: If you perform two possible unisons at once, then the one higher up on the
list will be the one executed.

Pow Blade
Cross Thrust
Power Thrust / Dark Serpent / Mirage Thrust
Stardust Rain
Lightning Punishment
Arch Wind
Lightning Tiger Blade / Photon Tempest
Pow Spear
Fiery Beast
Innocent Edge (could fit anywhere between Pow Spear and Mjollnir)
Mirage Infliction
Mjollnir
Moonlight Fury
Photon Blast
Plasma Blade / Prism Stars
Rock Pillar
Pow Devastation
Thunder Tiger Blade
Critical Blade
Wyrm Wrath
Savage Fury
Savage Mirage
Gospel
Gungnir
Purgatory Seal

The following combinations can't be compared directly against each other:

Critical Blade and Wyrm Wrath
Wyrm Wrath and Savage Fury
Savage Fury and Savage Mirage
Savage Mirage and Critical Blade

Q: How come when I use Stardust Rain, I don't get many hits at all?
A: Stardust Rain's hit percentage is base on the size of the enemy. The larger
the enemy, the more falling stars will hit. The position and shape of the
enemy are also factors.

Lloyd and Colette

Pow Blade

• Tiger Blade + Pow Hammer
  
• Heavy Tiger Blade + Pow Pow Hammer
  
• Tiger Rage + Pow Pow Hammer
  
• Twin Tiger Blade + Hammer Rain

Stardust Rain

• Sword Rain: Alpha + Hammer Rain
  
• Sonic Sword Rain + Hammer Rain

Lloyd and Genis

Fiery Beast

• Beast + Eruption
  
• Beast + Flame Lance
  
• Hunting Beast + Explosion
  
• Raging Beast + Explosion

Lightning Tiger Blade

• Tiger Blade + Lightning
  
• Heavy Tiger Blade + Thunder Blade
  
• Heavy Tiger Blade + Spark Wave
  
• Tiger Rage + Thunder Blade
  
• Tiger Rage + Spark Wave
  
• Twin Tiger Blade + Indignation

Lloyd and Raine

Photon Tempest

• Tempest + Photon
  
• Psi Tempest + Photon
  
• Omega Tempest + Photon

Gungnir

• Super Sonic Thrust + Ray
  
• Super Sonic Thrust + Holy Lance
  
• Hurricane Thrust + Ray
  
• Hurricane Thrust + Holy Lance

Lloyd and Presea

Innocent Edge

• Demonic Circle + Infinite Destruction
  
• Demonic Chaos + Infinite Destruction

Lloyd and Regal

Wyrm Wrath

• Demonic Circle + Eagle Rage
  
• Demonic Chaos + Eagle Rage

Lloyd and Sheena

Power Thrust

• Sonic Thrust + Power Seal
  
• Hurricane Thrust + Power Seal Pinion
  
• Super Sonic Thrust + Power Seal Absolute
  

Dark Serpent

• Sonic Thrust + Serpent Seal
  
• Hurricane Thrust + Serpent Seal Pinion
  
• Super Sonic Thrust + Serpent Seal Absolute

Mirage Thrust

• Sonic Thrust + Mirage Seal
  
• Hurricane Thrust + Mirage Seal Pinion
  
• Super Sonic Thrust + Mirage Seal Absolute
  

Lloyd and Kratos/Zelos

Cross Thrust

• Sonic Thrust + Sonic Thrust
  
• Huricane Thrust + Huricane Thrust
  
• Super Sonic Thrust + Super Sonic Thrust

Lightning Tiger Blade

• Tiger Blade + Lightning
  
• Heavy Tiger Blade + Thunder Blade
  
• Tiger Rage + Thunder Blade

Thunder Tiger Blade

• Tiger Blade + Lightning Blade
  
• Heavy Tiger Blade + Lightning Blade
  
• Tiger Rage + Lightning Blade
  
• Twin Tiger Blade + Super Lightning Blade
  
• Demonic Tiger Blade + Super Lightning Blade

Fiery Beast

• Beast + Eruption

Colette and Genis

Mjollnir

• Pow Hammer + Lightning
  
• Pow Pow Hammer + Thunder Blade
  
• Pow Pow Hammer + Spark Wave
  
• Hammer Rain + Indignation

Colette and Kratos/Zelos

Pow Spear

• Pow Hammer + Light Spear
  
• Pow Pow Hammer + Victory Light Spear
  
• Pow Pow Hammer + Light Spear Cannon
  
• Hammer Rain + Victory Light Spear
  
• Hammer Rain + Light Spear Cannon

Mjollnir

• Pow Hammer + Lightning
  
• Pow Pow Hammer + Thunder Blade

Colette and Presea

Pow Devastation

• Pow Hammer + Devastation
  
• Pow Pow Hammer + Mass Devastation
  
• Pow Pow Hammer + Finite Devastation
  
• Hammer Rain + Mass Devastation
  
• Hammer Rain + Finite Devastation

Colette and Raine

Photon Blast

• Ring Whirlwind + Photon
  
• Ring Cyclone + Photon
  
• Whirlwind Rush + Photon

Gospel

• Angel Feather + Ray
  
• Angel Feather + Holy Lance
  
• Judgement + Ray
  
• Judgement + Holy Lance
  
• Grand Cross + Ray
  
• Grand Cross + Holy Lance

Genis and Kratos/Zelos

Rock Pillar

• Grave + Grave
  
• Stalagmite + Grave
  
• Ground Dasher + Grave

Genis and Presea

Lightning Punishment

• Lightning + Punishment
  
• Thunder Blade + Dual Punishment
  
• Spark Wave + Finality Punishment
  
• Indignation + Rising Punishment

Critical Blade

• Explosion + Infinite Destruction
  
• Eruption + Deadly Destruction
  
• Eruption + Fiery Destruction

Genis and Raine

Prism Stars

• Ray + Tidal Wave
  
• Ray + Explosion
  
• Ray + Cyclone
  
• Ray + Ground Dasher
  
• Ray + Indignation

Raine and Kratos/Zelos

Plasma Blade

• Photon + Lightning Blade
  
• Photon + Super Lightning Blade

Gospel

• Ray + Angel Feather
  
• Ray + Judgement
  
• Holy Lance + Angel Feather
  
• Holy Lance + Judgement

Gungnir

• Ray + Super Sonic Thrust
  
• Ray + Hurricane Thrust
  
• Holy Lance + Super Sonic Thrust
  
• Holy Lance + Hurricane Thrust

Raine and Sheena

Purgatory Seal

• Ray + Demon Seal
  
• Holy Lance + Pyre Seal
  
• Holy Lance + Demon Seal

Sheena and Presea

Mirage Infliction

• Mirage Seal Absolute + Endless Infliction

Moonlight Fury

• Power Seal Absolute + Endless Infliction
  

Sheena and Regal

Savage Fury

• Power Seal Absolute + Swallow Dance
  

Savage Mirage

• Mirage Seal Absolute + Swallow Dance

Kratos/Zelos and Sheena

Power Thrust

• Sonic Thrust + Power Seal
  
• Hurricane Thrust + Power Seal Pinion
  
• Super Sonic Thrust + Power Seal Absolute
  

Dark Serpent

• Sonic Thrust + Serpent Seal
  
• Hurricane Thrust + Serpent Seal Pinion
  
• Super Sonic Thrust + Serpent Seal Absolute
  

Mirage Thrust

• Sonic Thrust + Mirage Seal
  
• Hurricane Thrust + Mirage Seal Pinion
  
• Super Sonic Thrust + Mirage Seal Absolute
  

Kratos/Zelos and Presea

Lightning Punishment

• Lightning + Punishment
  
• Thunder Blade + Dual Punishment

Arch Wind

• Hell Pyre + Punishment
  
• Hell Pyre + Dual Punishment
  
• Hell Pyre + Rising Punishment
  
• Hell Pyre + Finality Punishment