Sync is an in-game term which can be used to define one of two things, most notably synched actions (Attacks, Magic, Excel Acts and Arm Forces) and Rogress Sync Effect (in which a Child of Eesa syncs with up to three Rogress at a time). Sync (Action) can be divided in three major categories, depending on the party members performing the sync and, particularly with magic, the presence of raystones in the battle field: single sync (for Magic and regular attacks), party sync (for Magic and Excel Acts), and raystone sync (Magic only). It must be noted that both player characters and enemies are able to perform different syncs, most notably some bosses which sync Excel Acts.
Sync (Moves)[]
Sync (Moves) refers to any move in battle that can be chained, that is: regular attacks, magic, Excel Acts, and some command Arm Forces. Performing a Sync of such moves usually yields their chaining (Tandem Syncs), or an upgraded version of them (Party/Raystone Syncs).
Sync Attack (Chained Attack)[]
From a certain point in game, characters gain the ability to sync attacks, that is, to chain up to four attacks at the same target. When such a sync is activated, the attacks are chained upon the target in a separate animation, different from simple attacks, which transpire without interruption of the flow of the fight. Chained Attacks can only be done by a single party member on a single target.
Team Attack[]
A "particular" case of chained attack, it activates randomly when one or more allies are in attacking range of a foe which is being attaced by another party member. The second attacker strikes the foe immediately after the first one finishes his attack, without spending AP for doing so. This sequence of attacks takes place in a separate animation, as in regular chain attacks. Only the main/guest characters, and seemingly some bosses are able to perform this kind of sync. The use of the "Followup" Arm Force also enables such chains.
Sync Magic (Supreme Magic)[]
Like with Sync Attacks, you can only sync a single magic (that is, the same magic, of the same level, i.e.: have all involved characters sync Fireball for a Fiery Vortex) on a single target (or an area of effect magic with the center on the same target). Supreme Magic (which is the in-game name of sync magic) is the easiest to perform, since they can be performed by a single character using the same magic more than once in the same turn against the same target, any amount of characters using the same magic on a given target, and a character (or more than one) using magic in the presence of the appropriate raystone (that is, of the same element of the magic which is being cast. Regardless of its level, casting it in the presence of a fire raystone will always cause fire supreme magic, for instance). Supreme magic is an upgraded version of the cast magic, having its base effects augmented (like damage or duration) or additional side effects (such as added status disorders) in relation to the base form, and usually involves an additional animation during its execution. In terms of MP consumption, Supreme Magic will require an MP for each time the magic is cast, that is, if a character casts the same spell twice for a Supreme Magic, he/she will use 2 MP for the action. The same thing applies in regards to AP consumption. The Sync Rate (a percentage that appears at the bottom left of the screen during the Sync) indicates how effective the Sync was. Supreme Magic cast by more than one character will result in a Party Sync, that is, a single character (the Party Leader) casts the spell, with the other(s) playing a supporting role, without magic being chained. The MP and AP will be deducted from each character that helps in the Sync, but the AP recovery for the next round will be greater. Raystone sync bypasses the additional MP and AP requirement, but it must be noted that both characters and enemies can cast Supreme Magic if they Sync with a Raystone. It must also be noted here, however, that only bosses will use Single Sync Magic against the party, as regular foes might occasionally Party Sync their magic against a target.
Sync Excel Acts[]
Excel Acts can be synched from the same point in game where the other syncs become available, but they will only work when three characters use offensive Excel Acts on the same target. Excel Acts only Sync in Tandem, that is, they are chained, with one party member taking from where the last left off. The number of combo hits will increase as such, with no reset between the moves. The Action Cards, displayed on the bottom right of the screen, will only show the Party Leader, that is, the one in the chain of Excel Acts who goes first. The Sync Rate (a percentage that appears at the bottom left of the screen during the Sync) indicates how effective the Sync was.
Trinity Acts[]
From a certain point on in the game, the Excel Act sync will also produce a Trinity Act, which is a fourth move in the chain (which happens after the three Excel Acts) performed by all three characters which synched their EAs, led by the Party Leader. According to set prerequisites (%SP and AP consumption), one of two Trinity Acts will be performed: Mystic Fortune or Geo Impact, the last one being the most powerful (and costly) of the two. Some bosses in the game are also capable of performing Trinity Acts against the characters, and will do so, usually in the first rounds of combat. Though the game states that they are elemental-based (water and earth, respectively), both count as physical attacks, for the purposes of damage calculation, which means they do full damage even against foes which are resistant to said elements. The same thing applies to Excel Trinities, which are explained below.
Excel Trinities[]
Upon meeting certain other prerequisites (superior %SP and AP cost per move), characters will perform Excel Trinities, which are, in a sense, improved Trinity Acts, and are exclusive to each character. The Party Leader will perform the Excel Trinity, with the other two characters playing a supporting role. A given combination of Excel Acts will not always yield the same Excel Trinity, however, since a different Excel Trinity will likely happen when fighting against bosses. For instance: a combination of Ignis Beat, Acqua Spiral and Trickster usually results in Ryfia performing Luminoso, while fighting against a particular boss, however, the same combination led to L'Arc executing his Disaster Fang. Some bosses are also capable of chaining their Excel Acts into Excel Syncs, which function like Excel Trinities, save for the fact that they perform it through an independent (that is, not chained) Single Sync.
Arm Force Sync[]
The most unusual of the Syncs, Arm Force Syncs are usually performed using some Command Arm Forces together with attacks, such as using the Absorption Arm Force and the Attack command. These combined commands will enable the attack to have an additional side effect, much like other Arm Forces such as Add Confusion. Using the Steal Arm Force twice on the same target will cause the character to perform a Planned Steal (an upgraded version of Steal). It should be noted that not all Arm Forces can be chained, such as Morale Support or Taunting. These will just perform one command at a time, even if the player chooses to use it on the same ally/foe.
Rogress Sync Effect[]
Rogress Sync Effect is exclusive to the Children of Eesa. It is one of the effects of having bonded with Rogress, and composes a set of bonuses/penalties from having the bonded Rogress sync with them. Up to three Rogress (from the total available) can be synched at any given time in the game, and their bonuses/penalties add up. For instance, Gula has a +2 Earth, -2 wind resistance, and Papirusagu grants +2 wind, -2 Earth resistance (amongst other bonuses). If you Sync with them at the same time, both bonuses and penalties will cancel each other out.
Being in Sync with a Rogress also allows the Child of Eesa to summon it into the battlefield, where the Rogress will perform a move which affects the entire area, towards attacking the foes, or protecting/healing the party. Summon Rogress counts as magic in game mechanics, so if a Child of Eesa is silenced, the Summon Rogress option is blocked as well. Since Rogress summon depends on a single Rogress bar which is fully used up upon summoning, it cannot be chained.