La DEA of Libra:Functions

Functions (機能) are upgrades that cost points to unlock. Players are expected to unlock functions in order to become stronger and access more content.

How They Work
Interface 
 * You can unlock functions at any time outside ADV/battle by clicking on the circle in the upper-left corner of the screen, then clicking on blue circles corresponding to the functions you want.

Conditions Points
 * In addition to costing points, you must satisfy a function's unlock conditions before you're allowed to unlock it. A lot of the time, that means either progressing in the story or unlocking an adjacent function. Unlock conditions are all irreversible, nothing like "have X ingredients". Each function has a hint about the condition to unlock it, and once the condition is met, it will also reveal what it was.
 * Function unlock points can be obtained by battling or completing quests. The number of points gained from battle seems to be based on the strength and number of enemies defeated. 999 unlock points is the maximum amount of points.

Types
You can see the type by looking at what's written on top of the small blue/red/black circles in the function unlock screen.

Portrait - These are periodically unlocked over the course of the story, and can be any type of upgrade.

Skill (スキル) - Gives a particular character a particular skill (equippable passive effect), or if they already have that skill, increases it one level.

Map (マップ) - Adds icons to the mini-map. There are only 3 of these, and they can all be unlocked in the prologue. Very useful.

City (街) - Adds or upgrades an in-city feature like alchemy, a shop upgrade, or new quests,

Labyrinth (迷宮) - Adds an ability that can be used inside labyrinths, like Caula's wall destruction and Suri's harvest.

Feat (特技 ) - Adds new magical and physical techniques that can be used in battle. The type of technique is indicated, but what specific techniques will be learned isn't stated up front.

Possession (憑依) - Increases the number of points a specific character can allot to equip captured monsters.

Goddess (女神) - Increases the max value of the goddess gauge or decrease the gauge usage.

Battle (戦闘) - Grant some battle-related ability or improvement.

Fighting Spirit (戦意) - Grants some fighting spirit-related ability or improvement.

Level Limit (ＬＶ上限) - Increases the max level of all characters.