Fight as sub-characters:
Complete decisive battle (story) mode and keep both sub-characters alive. The sub-characters may now be used in any other game mode.

Fight as Katze:
Select a Shainto fighter and complete slash mode in under fifteen minutes. Katze will now be selectable under versus, group battle, and link modes.

Fight as Tsubame:
Select a Narukagami fighter and complete slash mode in under fifteen minutes. Katze will now be selectable under versus, group battle, and link modes.

Chanbarra mode:
Defeat all thirteen Bosses in action (Boss) mode without using any continues. Highlight the "Link Mode" option on the main menu and press Down(2) to access Chanbarra mode.

Hundred slashes mode:
Complete the game with the six regular characters.

Slash Mode:
To unlock slash mode you simply have to get eight of the twelve supporting characters. It does not matter which ones.

Kabuki Characters:
By beating the slash mode without dying you will aquire one kabuki character per school. This means you have to pick one fighter from each school and defeat the mode twice. The time doesn't matter and I would suggest Suminagashi from the Narucagami school and Gengoro from the Shainto school.