It is similar to the Rescue command as two units become one singular unit. Unlike the Rescue command, Pair Ups do not give negative bonuses to the lead character, instead giving them bonuses to their stats along with other effects. Stat boosts are determined by the supporting character's current class, their actual standard character bonuses, and the support level between the two. For example, if a Swordmaster pairs up to a General, the General will gain boosts in most of its stats, but Speed and Skill will be boosted more as it is the Swordmaster's better skill stats.
Pair Up units will always engage in a Dual System battle, even if there are units adjacent to them. Pair Up units can freely change who is the leading character between the two by using the Switch command. This allows players to use the character best suited to attack or to change a supporting character's equipped weapon. Players can Switch between Pair Up units as many time as they desire during a turn, given that they do not move and use the End command. They also have the Transfer command allowing a Pair Up unit to either transfer their supporting unit to an adjacent non-Pair Up unit or swap supporting units with an adjacent Pair Up unit. Transferring units will end the turn for the unit team that initiated the command. The last function they have is the Separate command, allowing the Pair Up to separate from each other and become solo units once more. Separating characters leaves the current lead character in the spot where they separated. The supporting character can be placed on any adjacent terrain that they can move on. Separating Pair Up units will end both unit's turns.
Having units in a Pair Up can boost Supports Levels when the units engage in battle, and the bonuses are better than adjacent Dual System support battle. This only applies for units that can support with each other; for example, if unit A can support with unit B and has an S-Support rank with them, the boosts will be much more greater then that of a C-Support rank. If used with units that cannot support with each other, only one boost, Hit +10 is used unless either unit has Dual Support+. After the lead unit attacks in a Pair Up, either the enemy attacks or the supporting unit attacks (it can miss). When an enemy attacks the lead unit, the supporting unit can block the incoming attack. The chances of this occurring increase based on their Support rank with each other.
A Pair Up can walk into an Event Tile, and if those two units can support with each other a short conversation will occur between them, increasing support levels by 9 points. In a fight involving a Pair Up, only the lead unit can use any skill that they have available at the start of the battle. The supporting unit however, cannot use skills such as Lethality but certain passive skills on the supporting unit, such as Hex and Solidarity, will still work. Supporting units that attack do not cause the opponent to activate Counter or Miracle.
After Robin activates this move, Chrom will warp into the stage and will rush forward as his critical/skill cut-in flashes onto the stage. Chrom will rush approximately 1/3 the distance of Final Destination and any Enemy he connects with will be launched into the air. Robin and Chrom then attacks the enemy, Chrom attacking with a series of slashes from his Falchion while Robin unleashes a barrage of various spells onto the enemy. The Final Smash ends with Robin equipping a Bolganone tome before the duo spikes the enemy to the ground. Spike has a high rebound, and the KO potential is largely based on the damage percentage on the enemy and their weight. The move will deal a maximum of 45% damage and can KO an opponent at as low as 45%. If Pair Up connects, Robin's Levin Sword and Tomes will return to full durability.