Easy mode
Start a game and die three times. If done correctly, a message will appear to indicate that a new easy difficulty setting is available. Note: You cannot achieve an "Onimusha" rank when playing in easy mode.

Hard mode
Successfully complete the game on the normal difficulty setting to unlock the hard difficulty setting.

Kick ass mode
Successfully complete the game on the hard difficulty setting to unlock the kick ass difficulty setting.

Ending bonuses
Successfully complete the game to unlock the Scenario Route option, Man In Black Suit mini-game, and Team Onimusha mode.

Critical mode
Successfully complete Team Onimusha mode to unlock critical mode.

Strongest equipment mode
Successfully complete the game on the hard difficulty setting. Then, start new game to begin with the Blazing Fire Sword, 20,000 in money, 30 Intense Medicines, 10 Wood, all level 3 armors, infinite ammunition, and skill always full.

Mind twister mode
Successfully complete the game with all eighteen artworks to unlock mind twister mode.

Leather costume
Successfully complete the game with the "Onimusha" rank to unlock a leather costume.

Oyuu's alternate costume
Get a 100% scenario completion to unlock an alternate costume for Oyuu.