(at around 18 mins) For the sequence based on the part in the manga during chapters 13-16 of volume 2, where a naked Susuki of the Funakigumi is tortured by being suspended from meat-hooks. Susuki's actor Susumu Terajima required twelve hours of makeup and other preparation, and then spent twelve more hours shooting the scene.
(at around 4 mins) Director Takashi Miike reveals on the U.S. TokyoShock DVD release that Ichi's semen used in the close-up during the intro sequence, when the film's title raises out of a puddle of semen, is actually real.
As a publicity gimmick, barf bags were recieved by viewers out at the Toronto International Film Festival (TIFF) to those attending the midnight screening of this movie. Similar bags were given during the Stockholm International Film Festival. Reportedly watching this film caused one viewer to throw up and another to faint.
Ichi is a Japanese number meaning "one," which is why Shiroishi "Ichi" Hajimé has the number 1 on the back-padding of his extreme sports body armor and the vertical razor on Ichi's bladed backstay boot also resembles the number 1.
Director Takashi Miike originally intended to have the author of the original shinen manga (comic book), Hideo Yamamoto, to write a script entirely in manga form, but the idea fell through when Yamamoto felt he could not complete it due to writer's block.