Gungrave Overdose [PSX]

Play As Rocketbilly Redcadillac
Successfully complete level 1 as Beyond The Grave.

Play As Jyuji Kabane
Successfully complete level 1 as Beyond The Grave.

Extra Features
Get alternate (last boss) costumes, the sound test, stage select, movie viewer, and enemy rush by clearing the game with all three characters on any difficulty.

Customize Options
The customize options are awarded as players earn skull points through exceptional gameplay in the following areas:

Art Points
Beat count
Jackpots
Number of kills
Stage clear time

Get a high enough score in each of the five categories to earn skull points which will accumulate. Accumulate enough and the various options (called 'features' in the US version) will be unlocked on the stage statistics screen.