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 mode, Team Onimusha mode, and the Puzzle Illusion Dream Dimension mini-game.
Team Onimusha one hit kills:
Successfully complete the game in Team Onimusha mode to unlock an option to replay Team Onimusha with one hit kills.
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.
Special secret:
While in the town of Imasho, trade with the other characters until you get three fossilized bones. Later in the game, after you teleport from Gifu Castle back to the Oni Sacred Place, you will find two doors in the second room. Place the bones in the middle door to reveal a secret.
Issen kill for all onscreen enemies:
Get the book of Tech 2 so you can charge up any of your weapons three times. Then, performed the Issen kill, but continue holding (Square). Jubei will do the Issen kill for all enemies on the screen. o this on a lesser enemy such as a Crocodile Man or Rolling Orc to get the much larger one.
Instant kill:
To instantly kill any normal enemy, walk near them and wait until they try to strike you. Just before it is about to hit you, tap (Attack) and a yellow streak will instantly kill the enemy. Note: This attack does not work on Bosses.