Construction allows the user to conjure an object from nothing. Unlike creating objects within a Domain, things constructed by this technique will not disappear once the spell has finished. However, creating something from nothing uses an immense amount of cursed energy, which results in harsh backlash on the user's body.
Mai developed this technique and hid it from her twin sister, Maki during their upbringing. She uses a revolver in battle, so after shooting six shots against Maki it appears she's out of bullets. However, construction allows her to load another cursed energy charged bullet into her gun. This surprise attack is meant to take the opponent off guard and finish the fight.