In order to unlock the following characters, beat the game with a different character the prescribed number of times:

Kim Kaphwan - 1 time Richard Myer - 2 times Fio - 3 times Hanzo Hattori - 4 times B. Jenet - 5 times Nightmare Geese - 6 times Ninon Beart - 7 times Lilly Kane - 8 times Classic Kyo Kusanagi - 9 times Wild Wolf - 10 times Armor Ralf - 11 times Mr Karate - 12 times Hyena - 13 times Jivatma - 14 times