"Game Over" twice in normal mode, and easy mode will be unlocked
Complete the game on normal mode once
Complete game on hard mode once
Oni Hard mode:
Complete Issen mode once
Complete the shooting mini game
The three swords from Onimusha 1
Complete all of the phantim realms, finish the game once, and start new game.
Finish the game once on any difficulty
Puzzle mini game C
omplete all puzzles in the normal game
Secret training mode:
Complete normal training mode once and unlock it after
finishing the game
Shooting mini game:
Finish game once on 'Normal' difficulty
Infinite 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.
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.
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.
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.
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.