Here you can find the list of unlockable characters and other stuff. To unlock them, you should do the following:
Becky: Defeat Candy Cane 10 times while playing as Miss Spencer
Noble Rose: Defeat Evil Rose 10 times while playing as Reiko Hinomoto
Yasha: Defeat Benikage 10 times while playing as Anesthesia
Eva's Gear from 'Metal Gear Solid 3': Defend the belt 5 times
Photo Shoot Mode: Earn 8,000 cash then buy the camera in the shop
Sound Test in Locker Room: Earn 9,000 cash then buy the audio set in the shop