Complete Story Mode with any character, then highlight that person while at the Character Selection Screen and press Circle.  (Press Triangle in the Japanese version of the game).

Reset In-Game

Press Start + Select during game play to return to the "Fight" menu.

Fight as Goemon

Complete Okuni's campaign story.

Fight as Keichi Maeda

Complete Kenshin Uesugi's campaign story.

Fight as Kunoichi

Complete Hattori's campaign story.

Fight as Magoichi

Complete any character's campaign story.

Fight as Masamune

Complete two character's campaign stories.

Fight as Nobunaga Oda

Complete Oichi's, Magoichi's, and Noh's campaign stories.

Fight as Noh

Complete Ranmaru Mori's campaign story.

Fight as Okuni

Complete Keiji Maeda's campaign story.

Fight as Ranmaru Mori

Complete Mitsuhide Akechi's campaign story.

Fight as Shingen

Complete Sanada's campaign story.

Use the Death Element on your Weapons

Collect five volumes of the Book of Five Rings with a created character.