Shingo
Defeat Rugal in Team Attack mode.

King
Defeat Rugal in Single Attack mode.

Goenitz
Beat level 30 of Time Attack and hold R1 over Rugal on the select screen.

Geese
Beat level 40 of Time Attack and hold R1 over Billy on the select screen.

Riot Iori
Beat level 20 of Time Attack (hold R1 over normal Iori to select).