Complete the eastern mission of Chapter 3 in Weapon Master mode. The last stage will pit you against Cervantes. Defeating him allows you to play him in all modes.
Unlock Characters in Weapon Master Mode (Import):
Play through Weapon Master mode to unlock characters, modes and stages. As you beat a character in Weapon Master Mode, that character will be unlocked for use in other modes. Unlockable characters include:
Unlock Seung Mina:
In chapter 6 of weapon master mode, a palace icon will be in the middle. Fight Seung Mina there, win, and unlock the Korean princess for play in all modes.
When you tire of playing with her little sister, you can unlock a playable Sophitia by whacking her silly in Weapon Mode.
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