Die three times after starting a new game. A message will appear to indicate that a new easy difficulty setting is available if the cheat was successful. Note: You cannot achieve an "Onimusha" rank when playing in easy mode.
Complete the game on the normal difficulty setting.
Kick Ass Mode
Complete the game on the hard difficulty setting.
Complete the game to unlock the Scenario Route option, Man In Black Suit mini-game, and Team Onimusha mode.
Complete Team Onimusha mode.
Strongest Equipment Mode
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
Complete the game with all eighteen artworks.
Complete the game with the "Onimusha" rank.
Oyuu's Alternate Costume
Get a 100% scenario completion.