The 4th Accessory slot for each character will be in whichever primary role hasn't already unlocked an extra Accessory slot. . I just started Chapter 12 and I still only have 3 accessory spots for each character. 4 accessories (1 by default and 3 through upgrades in the Chrystarium, though 3 is the max prior to beating the game). When and how do I get the 4th? In few words, it's just a way for the game to reduce you capacity to wear anything, anytime; because you have 4 slots for accessories and some.