Unlock Easy Mode
Begin a game and die approximately 5 times using the normal difficulty setting. After a few deaths, a message will tell you that easy mode is now available. Note: It is not possible to acheive an S rank in easy mode.

Unlock Difficult Mode
Complete the game in less than three hours.

Unlock Ultimate Mode
Complete the game on Hard Mode with any ranking other than S.

Go to: Genma Onimusha Info Page | nGaming Home Page.