Nails manipulated with the Straw Doll Technique can use Hairpin to greatly enhance their output of cursed energy. Cursed energy shrouding the nails expands with explosive force, highly magnifying their destructive capabilities.
Hairpin can be used to make use of nails that failed to hit their target by using explosions to affect the environment. Nobara first used the technique during the Goodwill Event during her fight with Momo Nishimiya. The Kyoto student's technique allowed her to stay out of Nobara's range. Hairpin destroyed several trees surrounding Momo, which forced her opponent much closer to the ground.
Nobara used it as a finishing move during her fight alongside Yuji against Eso and Kechizu. After striking Kechizu with Black Flash to grievously injure the Death Painting Womb, Nobara ended him with Hairpin before he could counterattack.
In Shibuya, Nobara used Hairpin to destroy an alley sign after kicking it into Mahito, drawing first blood in their duel. Then she used Hairpin twice within just a few moments after dropping several nails at Mahito's feet. The first activation knocked the nails upright and the second successively expanded their cursed energy into Mahito's lower body, immobilizing him for a moment.