How do you unlock the grey king on dynasty warriors 6 for PS3?

To unlock the Grey King in Dynasty Warriors 6 for PS3, you need to complete the game's story mode with all characters, ensuring that you reach the "True Ending" for each storyline. After finishing this, you can access the character selection screen, where the Grey King will be available for play. Additionally, make sure to meet any required conditions specific to the character, such as completing certain missions or challenges.