When you place two or more units adjacent to each another on the map, they will support each other in combat.
A character who is supported will receive a boost to his or her combat stats, depending on the number of adjacent units and the strength of their support relationships (see the next page).
Furthermore, when the character fights an enemy, one of the of the adjacent units will appear next to them as a "support unit".
When the character strikes the enemy, there is a chance that the support unit will attack as well -- this is called a Dual Strike.
When the enemy strikes your character, there is a chance the support unit will jump in and block your character from taking damage altogether -- this is called a Dual Guard.
As you plan your moves, it's wise to keep characters close to one another to make use of these support actions. Sometimes a well-timed Dual Strike can help you defeat enemies faster than usual, while a lucky Dual Guard could be the difference between life and death...
When playing on Normal Mode, the option to pair up is disabled until a certain chapter. However you can enable it instantly by going to Options and turning off the Tutorial.
New to this game is the ability to pair two characters together on the map to create a single, more powerful unit.
To pair up characters, simply move one character next to the other and choose the "Pair Up" option. The character who you moved will merge with the other and the two characters will move and act as one.
The initial character will become a support unit -- they will be safe from enemy attacks, but also unable to act on their own.
The other character, meanwhile, will become the main unit of the pair. He or she will receive a significant boost to their stats, which will be shown on their status screen. The stronger the support relationship, the better the boost.
Additionally, when the character pair engages the enemy, the main unit will automatically receive the same benefits as if they were fighting adjacent to the support unit -- this includes the Dual Strike and Dual Guard abilities.
Pairing up is a good way to make characters stronger and streamline your army's movements. For instance, instead of moving 10 units, you can just move 5 paired up units. Of course, the disadvantage is that you'll have less units at your disposal.
Whether or not to pair up depends on how confident you feel and how many immediate enemies you need to fight. If there are only 5 enemies nearby, you might be better off with 5 stronger, paired up units, for example. When there are lots of enemies trying to swarm you, it might be wiser to form walls with 10 weaker, separated units.