If you're referring to his S-Craft in Cold Steel 2, you need to purchase a certain item in the final dungeon that "transforms" one of your party members into Crow, thus allowing you to use him for the final dungeon. If you're referring to his 2nd S-Craft in Cold Steel 4, I believe everyone's S-Craft gets upgraded once they reach a certain level. Just be sure to swap your party members around to ensure that the new craft/S-Craft gets unlocked.