Naomi Karpati participated in extensive training exercises where she was able to hone knife and gun skills.
The flashback re-training and torture scenes were performed with great authenticity. Naomi Karpati was actually water-boarded and much of the physical assaulting was done with real contact.
A few days after filming the foot-chase / fight scene between Naomi Karpati and Yuki Ise, the abandoned warehouse complex location partly burned down claiming the life of a homeless person and was declared a crime scene.
The weapon of choice for Naomi Karpati's character Alex, was either the 9mm Browning or Beretta 92.