Easy mode:
Start a game and die three times. 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 under the normal difficulty setting.

Ending bonuses:
Successfully complete the game to unlock the Scenario Route option, Man In Black Suit mini-game, Oni Organization mini-game, and the Puzzle Illusion Dream Dimension mini-game.

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

Issen mode:
Successfully complete the Oni Organization mini-game. You must hit with a One Flash attack in order to do damage to opponents.

Puzzle Illusion Dream Dimension:
Successfully complete the game with all Paintings Of Beauties.

Leather costume:
Successfully complete the game with the Onimusha rank.

Oyuu's alternate costume:
Get a 100% scenario completion.