True to its name, it is a counterattack. The Mii Swordfighter will lean back and hold its sword in reverse grip upon activating, and if hit with an attack while in this pose, retaliate with a slash of the weapon. The move does 1.25x the damage of the attack that hits the Swordfighter, with a minimum of 8% damage. When the move is initiated, a jagged red line appears upon countering an attack, resembling the one that appears during Little Mac's Slip Counter.
In Ultimate, the counterattack has been altered: the retaliating slash is now an upwards lifting slash that sends opponents vertically. This gives it consistent KO potential regardless of the Swordfighter's positioning, but makes it significantly worse for KOing opponents near the side blast lines. Uniquely, the Swordfighter is shown "parrying" during Blade Counter with a twirl of their sword, which triggers an "off-balance" animation for the opponent and cancels their attack animation before the counterattack hits.
Special Move customization was added in Super Smash Bros. 4. These are the variations: