Robin summons Chrom through a warp circle. Chrom will travel a set distance from where he is summoned (a little less than half the length of Final Destination), and swipe at the first opponent in his path. If he misses, the Final Smash will fail. When he does catch at least one opponent, Chrom's critical hit portrait from Fire Emblem Awakening appears as he yells "On my mark!" (俺に合わせろ！, Join with me!). Once an opponent is caught, the two unleash their attacks: Chrom with the Falchion, and Robin circling the unfortunate foe while unleashing Bolganone and Thunder, assailing the opponent multiple times. Finally, just as Robin shouts out the name of their spell followed by Chrom yelling "We're not done yet!" (食らえ~!, Eat this~!) the two strike the opponent(s) at the same time, rocketing the foe(s) to the ground and rebounding towards the upper blast line.
This attack ends up dealing 45% damage - 5% with the initial strike, 26% for the flurry of attacks (13 strikes at 2% damage each), and 14% for the finishing strike. The knockback from the final blow cannot be teched. It can KO an opponent with at least 45% damage under average circumstances. The move elevates Robin and Chrom to the highest point on the stage and always takes place in the center of the stage, except for stages that can cause an OHKO due to the map having a central pit (examples include Gaur Plain and Midgar after Odin's attack). On stages with a high upper platform such as 75m and Boxing Ring, it is essentially a guaranteed OHKO because the opponent is brought up to the top platform, very close to the stage boundary.
Successfully using the Final Smash will restore Robin's Levin Sword and all his tomes to full durability. Overall, the attack is very akin to Ike's Great Aether, only Robin stays in midair when the move ends, risking much less of a self-destruct in comparison.
Like the Pair Up feature in Fire Emblem Awakening that lets two characters attack a foe at once, Robin's Final Smash calls Chrom, the Prince of Ylisse, to the battlefield. First, Chrom dashes forward, and if he lands a hit, Robin joins him for a flawless combination of attacks. It can even catch multiple opponents at once!
Chrom, one of the main protagonists in Fire Emblem Awakening, joins Robin to attack the opponents, reflecting a mechanic first introduced in Awakening where two units can pair up. The supporting unit can not only boost combat stats, but they can also attack after the main unit, or can block enemy attacks from reaching the main unit. Chrom's portrait that appears is also derived from Awakening: when a skill or a critical hit activates, the character's portrait is shown and accompanied with a spoken one-liner from that character (though interestingly, "On my mark" is not one of Chrom's portrait one-liners, but rather one of the things he says at the beginning of a battle sequence if he is supporting the main unit). After the series of hits, Robin proceeds to shout "Bolganone", which Chrom follows by shouting "We're not done yet!", another battle quote from Awakening, but in SSB4, he shouts it in a fiercer manner. Fittingly enough, the Pair Up maneuver was invented by Robin himself.