When you summon a GF in battle, a blue bar will replace your ATB bar and will deplete. Once depleted, the GF will appear, but during the period while the bar is depleted all attacks directed at the summoning character will damage the GF, instead. If a GF’s HP are depleted during summoning, that GF will be KO’d and unable to be summoned until you rest or use a restorative item to bring it back, such as a G-Returner.
All pretty straight-forward stuff, but the speed at which a GF is summoned (the rate at which the blue summoning meter is depleted) is determined by a "Compatibility" stat, which essentially rates how well a GF and a specific character get along. GFs have different preferences, which influence their starting Compatibility, and you can also influence a GF’s Compatibility - negatively and positively - by summoning other GFs, casting certain spells, or using items. Turns out a fire GF might not be happy if you cast Blizzard, or summon that nasty ice GF, and while GFs are fickle and let their politics affect their disposition towards you, it’s generally not all that hard to butter them up by using certain items.
The difference in summoning speed can be quite drastic between a GF at low Compatibility and one at high Compatibility At the lowest Compatibility (0), a GF might take 17 seconds to arrive, while at the highest Compatibility (1,000) a GF can arrive in around 3 seconds. This summoning rate is fairly balanced across the Compatibility spectrum, as at 500 Compatibility a GF will take around 10 seconds to show up. That said, you probably won’t have many GFs on one character that you’ll summon often, ans since summoning a specific GF increases Compatibility with that GF, it shouldn’t be hard for you to boost the Compatibility of the GFs regularly used by each character, should you see the need to do so.
All in all, you’re probably not going to lose a fight if your Compatibility with a GF is low, or win one if it’s high, but in the few instances where using a GF is a noticeable boon, it can help to know how this works. Can’t hurt to have an edge, however slight, right?
Below you’ll find the starting Compatibilities of all the GFs and characters, information that’s more interesting than useful. In most cases, the difference between a character a GF dislikes and one a GF likes is a matter of maybe a second. Nothing to lose sleep over.
As mentioned earlier, not all GFs are friends with each other. In fact, most GFs have another GF to which they’re opposed. Whenever you summon a GF, it’ll gain +20 Compatibility, while other GFs will lose -1.6 Compatibility The GF opposed to the one you summoned, however, will lose -10 Compatibility The only exception to this is Eden, which gains a paltry +2 Compatibility whenever it’s summoned, while other GFs gain +1 Compatibility
|Guardian Force||Opposed Guardian Force|
Most GFs have an item you can use to increase the user’s Compatibility with said GF. Typically this item increases the GF’s Compatibility by +3.2, bot lowers the character’s Compatibility with all other GFs by -1.6, although some items (Arctic Wind, Bomb Fragment, Poison Powder and Shear Feather) give half the normal boost/penalty, while the Fish Fin item gives +2 Compatibility with Leviathan, but -1 Compatibility to all other GFs. Less mixed, using a LuvLuvG item will increase a character’s compatibility with all GFs by +20. You can refine the Chubby Chocobo Card for 100x LuvLuvGs, which is enough to boost each character’s Compatibility with all GFs by +320.
|Guardian Force||Compatibility Items|
|Shiva||Arctic Wind, North Wind|
|Ifrit||Bomb Fragment, Red Fang|
|Pandemona||Shear Feather, Windmill|
|Doomtrain||Poison Powder, Venom Fang|
Last and certainly least, GFs are sensitive to what spells you cast. Casting a spell in the "Favored Magic" column will earn you Compatibility, while casting spells in the "Opposed Magic" column will lose you Compatibility, but in this case… well, we’re talking about a +2 bonus or -2 penalty, at best/worst.
|Guardian Force||Favored Magic||Opposed Magic|
|Quezacotl||Aero, Thunder, Thundara, Thundaga, Tornado||Water|
|Shiva||Blizzard, Blizzara, Blizzaga||Fire, Fira, Firaga|
|Ifrit||Fire, Fira, Firaga||Blizzard, Blizzara, Blizzaga|
|Siren||Berserk, Blind, Break, Confuse, Pain, Silence, Sleep, Slow, Stop||Dispel, Esuna|
|Brothers||Flare, Meteor, Quake, Ultima||Aero, Float, Tornado|
|Diablos||Demi, Flare, Meteor, Ultima||Dispel, Esuna, Protect, Reflect, Shell|
|Carbuncle||Aura, Cure, Cura, Curaga, Double, Esuna, Full-Life, Haste, Holy, Life, Protect, Reflect, Regen, Shell, Triple||Berserk, Blind, Break, Death, Dispel, Pain, Silence, Sleep, Slow, Stop, Zombie|
|Leviathan||Flare, Holy, Meteor, Ultima, Water||Thunder, Thundara, Thundaga|
|Pandemona||Aero, Tornado, Ultima||Water|
|Cerberus||Aura, Dispel, Double, Esuna, Haste, Protect, Reflect, Shell, Triple, Ultima||Berserk, Blind, Break, Confuse, Pain, Silence, Sleep, Slow, Stop|
|Alexander||Curaga, Full-Life, Holy, Life, Regen, Ultima||Bio|
|Doomtrain||Berserk, Bio, Blind, Break, Confuse, Death, Silence, Sleep, Slow, Stop, Ultima, Zombie||Holy|
|Bahamut||Flare, Holy, Meteor, Quake, Tornado, Ultima||--|
|Eden||Flare, Holy, Meteor, Quake, Tornado, Ultima||Aura, Blizzard, Blizzara, Cure, Cura, Curaga, Dispel, Double, Esuna, Fire, Fira, Full-Life, Haste, Life, Protect, Reflect, Regen, Shell, Slow, Thunder, Thundara, Triple|