Complete the game on hard to unlock Samanosuke's other costume.
Complete the game with an S ranking by finding all of the Fluorites to open up Kaede's other costume.

When you start a new game, die five to six times on the normal difficulty setting. (You won't be able to get an S-rank though)

Complete the game in under three hours.

Complete the game on hard with any rank achieved except S. Or complete the Onimusha Spirits mini-game.

Complete the game in difficult mode and you cannot use the Bishamon Sword, pick up and equip the Ogre Armor, and collect all of the Fluorites.