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 used a revolver in battle, so after shooting six shots against Maki it appeared that she had ran out of bullets. However, the construction allowed her to load another cursed energy charged bullet into her revolver. This surprise attack was meant to take her opponent off guard and finish the fight.
Mai's limit was one bullet per day, but this drained what little cursed energy she possessed, resulting in physical backlash such as a nose bleed. even that causing her nose to bleed After being cut open by her own father, Mai decided to use construction to give her sister Maki a fighting chance. Mai was aware the backlash would kill her, but she used that opportunity to take all the cursed energy between the twins with her. Mai sacrificed her life to give Maki a body of steel that has escaped from cursed energy by utilizing construction to create a large broadsword.