Strangely enough... Lucien didn't get knocked back as Irina intended for him to. In fact, he moved himself accordingly to Irina's momentum in that small moment so that her dagger would become embedded in his stomach as he spun away from her. While doing this he used his sword hand to bash Irina's hand off of the dagger via pommel smashing her wrist with his katana. With the pistol, he fired a few point-blank shots at her chest - more shotgun shells. Either she would have to let go of the dagger to minimize the damage done to her by the point-blank shells or risk severe damage from Lucien's firearm.