Each GF can only be junctioned to one character at a time, though that character may be changed at any time outside of battle - even if the character isn't currently on screen with the party. While a GF is junctioned to a character, it gains affinity for that character, allowing summoning to occur with less and less delay. However, affinity may also be lost if there is more than one GF junctioned to the same character, and one is summoned more often. While junctioned in battle, GFs gain experience and ability points. Experience leads to physical evolution of the GF, including greater hit points and increased spell damage. .
Ability points allow the GF to learn new abilities.
If multiple GFs are junctioned to one character, the points gained are divided between the GFs. The player can direct the studies of each GF so that it will spend accrued ability points towards learning a particular ability. To do this select GF from the top-level option on the menu screen, and then select the particular GF desired. A list appears with all of the abilities that GF can learn. Abilities already known are marked as completed.