Samanosuke's alternate costume:  Successfully complete the game under the normal difficulty setting with a high score as Samanosuke. Alternately, successfully complete the game as Jacques' alternate costume.

Panda costume:  Successfully complete secret training mode. Alternately, play the game with a memory card with a saved game from Onimusha Blade Warriors .

Alternate ending sequence:  Increase all seven Haori of Ako to the maximum. This requires all Kodama to be found.

Easy difficulty:  Intentionally lose the game two times under the normal difficulty setting.

Hard difficulty:  Successfully complete the game under the normal difficulty setting.

Critical (Issen) mode:  Successfully complete the game under the hard difficulty setting. In this mode, only critical hits can kill opponents.

Oni Hard mode:  Successfully complete the game in Critical (Issen) mode.

Ultimate mode:  Successfully complete the Oni shooting mini game. The game will start with Sam having the Bishamon sword; Jacques having his best Oni Musou; unlimited arrows, bullets, unlimited Oni power, thirty Medicines, and ten Talismans.

Original Onimusha: Warlords swords:  Successfully complete the game with all three items from the Phantom Realms. Then, start a new game to have all three swords from the original Onimusha: Warlords .

Alternately, play the game with a memory card with a saved game from Onimusha: Warlords .

Bishamon sword:  Successfully complete the game with the "Onimusha" rank. Alternately, get the Bishamon sword in the Phantom Realm in Honnouji when Sam goes to the past. To find it, go to the save location at the foot of the stairs to the temple, then look to your upper left to find the hanging man. Approach him to be sent to the Phantom Realm. Collect eight Red Orbs to unlock the chest that contains the Bishamon sword.

Oni Musou:  Have Jacques go through the Phantom Realm in Honnouji.

Adventures of Heihachi (Heihachi Buraiden) mode:  Successfully complete the game. Heihachi (Honda) is now selectable.

Genma Puzzle mini game:  Solve all the puzzles in the game.

Secret training mode mini-game:  Successfully complete normal training mode, then complete the game.

Oni Shooting mini-game:  Successfully complete the game under the normal difficulty setting.

Ako's Black Haori:  Successfully complete Issen/Oni training.

Skip FMV sequences:  Successfully complete the game. When playing the game again, press Start to advance past any intermission sequence.

Defeating Guard Dog:  Note: This was done under the normal difficulty setting. First, stock up on magic for all your weapons. Then, stock up on all the Purple Souls. At the beginning, jump behind him after he attacks. Then, just waste the magic on him. Use every weapons magic until you do not have any more. After that, use regular attacks. Watch out for the ice attack. Most of the time the thunder magic from him is off target. After a few regular attacks, transform into the Onimusha and attack him hard. However, do not use the mega attack yet. After a few attacks, just before your magic runs out use the mega magic attack on him. If he is not defeated, then just attack him a few more times.

Defeating Nobunaga:  When you are fighting Nobunaga when he is in his demon form, press Square (2), Triangle . This is a great combo move, but do not overdo it with him. When you absorb the darkness from his sword and you get it, remember that some of his moves cannot be blocked (such as the charge and the fireball moves). You can only block one or two. For the charge move, press Triangle at the last moment when he is on fire and you should dodge it. For the fireball move, just have enough space to run around.

Defeating Two Marquless:  When playing as Michelle, go further behind near the skull door and throw some grenades on them.

Kill all Genma onscreen:  Level up your Oni Gauntlet to level 3.Then,when there are a lot of Genma, charge your weapon to level 3 or until it is purple. When a Genma attacks, do a critical while the weapon is still charged. Note: Deflect Critical does not work -- only Critical. This most useful at the Dark Realms and Azuchi Castle.

This can be done without charging during an Onimusha. Also, block Issen works during an Onimusha and takes out all enemies.

Regain health:  Equip Ako's White Haori then stand still.

When Ako's wearing the White Haori, rotate the Right Analog-stick . Ako will move faster to regain health quicker, depending how fast you can rotate. Note: Do not not use it while you have five Oni Orbs.

Deflecting critical hits:  Repeatedly tap Guard until someone hits you. And as soon as you see the flash, tap Square . Keep tapping Square to go from enemy to enemy, racking up multiple critical hits.

Unlimited Genma Souls:  After going through the first set of double doors where the Oni Army is fighting the Genma, before using the Firefly to go up the short cliff, have the Genma and and Oni Army men on the wall of the short cliff and you as close as possible to the doors on the other side of the field. The supply of Genma infantry are infinite and Oni Army can take care of them by themselves. While they are fighting and nowhere near you, tape down Circle and allow the game to run. The souls will come to you, and you can get as many as desired without interruptions from the Genma. For a slightly faster collection, have Ako's Blue Vest equipped. Note: The process of getting a lot of bars filled of souls will take a long time. Also, when the soul count reaches 9,999, release Circle . This gives you an additional bar (or perhaps more) filled automatically. Then, tape Circle again. Given enough time you can have 99 bars worth of souls.

Note: This trick only works for Samanosuke. Once you obtain the Ten-Point Slash Training Scroll, play under the beginner difficulty setting multiple times. Each time you finish, you should come away with one bar, or close to it. Do this until you have the desired amount of souls, or until you max all your equipment.

Bypass Dark Realms:  Any of the three Dark Realms can be easily bypassed. This requires some skill, Ako's Purple Vest, all weapons for the character, and all weapons been completely enhanced. Whether or not the gauntlet is completely enhanced is irrelevant. Before entering the Dark Realm, equip either Chigo (for Samanosuke) or Hyosai (for Jacques). The enemies that attack will appear in multiple waves. Just wait for all enemies to appear, then execute one magic attack. Absorb all the souls that appear. Ako's Purple Vest should allow you to do this as many times as necessary. However, if you are fighting large demons, you may need to get up close with either the Tenso (for Samanosuke) or the Enja (for Jacques). Note: A crucial part of this strategy is absorbing the souls. If you feel that you need Ako's Blue Vest as well, make sure to switch back and forth as appropriate. Also, it is much easier to go straight for the bottom part of the Dark Realm that you are in, as the tougher enemies are down there first. By doing this, you can use your magic efficiently on the tougher enemies and not have to worry about the weaker ones.

Use less magic during magic attacks:  This trick requires the gauntlet for Sam/Jacques to be at least level 2. Charge up the gauntlet (press R1 firmly) to at least two and unleash a magic attack. With the purple vest on Ako you can do about five magic attacks in a row instead of four.

Awards:

Bravery: Successfully complete the game without saving.
Critical: Kill over 40% of your enemies with critical hits.
Defense: Take less than 5,120 damage.
Explorer: Find all 23 Tengu chests.
Offense: Kill over 3,000 enemies.
Speed: Have a completion time of less than 5:00:00.

Code Breaker Codes

(M)aster Code (must be enabled):
9A14483C 18C7FC40

Have Full Purple Stock:
0A6E9978 00000005

Inf Ogre Power Gauge:
1A6B5F8D 00000500

Inf Onimusha Mode:
2ACF3AE2 24420000

Inf Sub Weapon:
2A0311B3 24420000

Inf Vitality:
2AE34DF7 00000500

Max Ogre Power Gauge:
1A695F8D 00000500

Max Oni Gauntlet Level:
0AD2AA97 00000002

Max Red Armor Level:
0AD3AA97 00000002

Max Second Weapon Level:
0ADDAA97 00000002

Max Souls:
1A655F8D 0000FFFF

Max Sub Weapon:
1A354D29 00000063

Max Tenso Level:
0ADEAA97 00000002

Max Total Enhancement Points:
1A615F8D 000F423F

Max Vitality:
2AE74DF7 00000500

Third Weapon Level:
0ADCAA97 00000002
All codes above from Rhashad Smalls.