Unlock Michelle's Secret Costume - Finish game once with best ranking(Onimusha)
Unlock Panda Costume - Complete the Secret training mode
Unlock Samanosuke Special Outfit #2 - Have an Onimusha Buraiden save game on your memory card
Unlock Special Outfit For Samanosuke And Jacques - Simply beat 'Normal Mode' once
Unlock Easy mode - Get 'Game Over' twice in normal mode
Unlock Hard mode - Complete the game on normal mode
Unlock Issen mode - Complete game on hard mode once
Unlock Oni Hard mode - Complete Issen mode once
Unlock Ultimate mode - Complete the shooting mini game
Unlock 3 Swords from Onimusha 1 - Collect the 3 key items from the Phantom Realms at Underwater Temple and Mont St. Michel. Then complete the game, and when you start over again, you should start with the three secret weapons which will be found at the same street where Samanosuke first transfers into the future.
Unlock Mini Games:
Unlock Heihachi Buraiden - Finish the game once on any difficulty
Unlock Puzzle mini game - Complete all puzzles in the normal game
Unlock Secret training mode - Complete normal training mode once and unlock it after finishing the game
Unlock Shooting mini game - Finish game once on Normal difficulty
Unlock True Ending:
Get all Haori for Ako
Quick Recovery: When you have Ako's White Vest equipped, rotate the right analog stick and your life will replenish twice as fast.
Find the Bishamon Sword:
Before your last encounter with Nobunaga, go to the save point at the bottom of the stairs to the temple. Look to your upper left. The crazy hanging man is right there. Move a little closer and you'll be, once again, warped to the demon world. Here, you'll have to find 8 red orbs to unlock the chest. Once you do, The Bishamon sword is yours.