Ichi the Killer (殺し屋１ Koroshiya Ichi?) is a 2001 Japanese film directed by Takashi Miike, written by Sakichi Sato, and based on Hideo Yamamoto's manga series of the same name. The film is notorious amongst moviegoers due to its extremely graphic violence. The film has received widespread controversy and is banned outright in several countries due to its high impact violence and graphic depictions of cruelty. In 2009, The Norwegian Media Authority reacted to the film and later classified the film as Rejected and banned the film due to "high impact violence and cruelty" and the film is still banned in Norway, but still available for home video purchase. The film has been banned outright in Malaysia since the film's distribution date in 2001 due to "very high impact violence & offensive depictions of cruelty" The film is banned uncut in Germany, and classified as "adults only" in a "heavily cut version".
While alone with a prostitute, crime lord Anjo is brutally murdered. As an expert cleaning crew run by Jijii (Shinya Tsukamoto) removes any trace of his body, Anjo's gang and the other crime lords assume he and the prostitute fled town with ¥3 million of the gang's money. Only Kakihara (Tadanobu Asano), Anjo's sadomasochistic enforcer, believes Anjo is still alive. Jijii feeds Kakihara rumors that suggest Suzuki (Susumu Terajima), a member of a rival clan, has kidnapped Anjo. Kakihara captures Suzuki and tortures him, but when Suzuki turns out to be innocent, Kakihara slices off the end of his own tongue and offers it to Suzuki's boss (Jun Kunimura) as penance.
Jijii, it is revealed, is secretly orchestrating events in order to pit yakuza clans against one another, with the help of Ichi (Nao Omori). Though a normally unassuming and cowardly young man, Ichi becomes homicidal and sexually aroused when enraged. Jijii is able to manipulate Ichi's weak personality by implanting several false memories — a high school rape in particular — and uses the unstable Ichi as an assassin. Other than killing Anjo, Ichi also kills a pimp who regularly brutalized a prostitute named Sailor that Ichi patronizes. When Sailor attacks him, Ichi kills her as well. Later, Ichi helps a boy named Takeshi by saving him from bullies; Takeshi is the son of Kaneko, one of Kakihara's henchmen.
Using Suzuki, Jijii manages to have Kakihara kicked out of the syndicate, but the entire Anjo gang defects with him. When he learns that Anjo was killed by Ichi, Kakihara kidnaps and tortures Kano, a former member of the Anjo gang who is helping Jijii. Kakihara also becomes fascinated by Ichi, imagining him to be someone who can truly fulfill his masochistic urges.
Kakihara enlists the help of a pair of corrupt twin police detectives, Jirô and Saburô (Suzuki Matsuo), to find Myu-Myu, a prostitute connected with Ryu Long, a member of Jijii's gang. Unable to get information from her through torture, Saburô sniffs her to get Long's scent and tracks him down. Though Long attempts to outrun the brothers, he is captured by Kakihara.
To turn Ichi into a complete killer, Jijii has Karen, Anjo's woman and Jijii's friend, seduce Ichi by pretending to be the woman in his false memory. When Ichi becomes confused by Karen's claims that she desired for him to rape her, he kills her. Jijii calls Kakihara to let him know Ichi is coming to kill him.
Kaneko, Kakihara and Ichi chase each other to a rooftop. Due to Jijii's psychological manipulation, Ichi believes that Kaneko is his brother and confronts him. Kaneko shoots the side of Ichi's leg, causing Ichi to slit Kaneko's throat in front of Takeshi. Takeshi attacks Ichi as he lies on the roof begging for forgiveness. Kakihara realizes Ichi cannot hurt him and inserts skewers into his ears to drown out Ichi's cries. Suddenly he sees that Ichi has chopped off Takeshi's head. Ichi charges Kakihara, embedding one of his razor-bladed boots in the center of his head. Kakihara falls from the roof to his death. However, when Jijii finds him, Kakihara has no wound in his head; he hallucinated Ichi's attack as he jumped to his death while Ichi cried.
Years later, Jijii's corpse hangs from a tree in a park. A young man resembling an older Takeshi leaves the park with a group of schoolchildren.