From Transistor Wiki
Starting at Level 4, and as you continue to level, you'll access new Permissions which will enable your character more slots to use Functions.
Permissions[edit | edit source]
|Authenticator||Enter Backdoors||Reveals hidden Backdoors throughout Cloudbank.|
|Cache||Passive Bonuses from Functions||Opens a Passive Slot for use with any Function.|
|System||+1 Upgrade Slot||Enables a secondary Upgrade Slot for an Active Slot.|
|Memory||+4 MEM||Allows more Functions to be installed simultaneously.|
Turn Based Combat