I Saw the Devil

I will kill you when you are in the most pain. When you're in the most pain and shivering out of fear, then I will kill you. That is a real revenge. A real, complete revenge.

I Saw the Devil is a 2010 Korean Revenge movie directed by Kim Ji-Woon (A Tale of Two Sisters, The Good, the Bad, the Weird). It stars Lee Byung-Hun as Kim Soo-Hyun, a government agent who swears to violently avenge the murder of his fiancée. Said crime was commited by Kyung-Chul Jang (Choi Min-Sik), a psychopath to whom kidnapping, raping and murdering young women come as easy as breathing. What ensues is a dangerous cat-and-mouse game in which both men vow to destroy one another's life.

Tropes used in I Saw the Devil include:

Agony of the Feet: Kyung-Chul's both feet. one has its Achilles Tendon cut, another steps on a fishing hook
Anti-Hero: Soo-Hyun, who doesn't seem to care that his plan for revenge also puts innocent bystanders in danger. At one point he lets Kyung-Chul rape someone long enough just so he could disrupt his enjoyment that much further.
Attempted Rape
Badass: Soo-Hyun, especially during the fight in the old mansion where he takes out Kyung-Chul and two other serial killers, all of whom were hunting him.
Bittersweet Ending Soo-Hyun manages to murder Chul-Jang, but then he realizes what he's become.
Bottomless Magazines: A mild case when Kyung-Chul shoots three times with a double barrel shotgun before reloading.
Bowdlerized: The Korean version was effectively censored by the Korea Media Rating Board; several shots of violence and some scenes depicting cannibalism had to be removed before being released. The international version is uncut and true to the director's intentions, however.
Cowboy Cop: Soo - Hyun.
Determinator: Soo-hyon, but not as much as Kyung-Chul.
Disposable Woman: Joo-Yun.
Film Noir
Glasgow Grin: Soo-Hyun gives this to one of the cannibals by ripping open his mouth with his bare hands.
Gorn: Duh
He Who Fights Monsters: Explored and discussed.
Hey, It's That Guy!: Choi Min-sik was probably recognized (by Western audiences at least) as "the guy from Oldboy."
I'm a Humanitarian: Kyung-Chul is friends with some cannibals.
Infant Immortality: Just about the first thing the film does is subvert this.
It Got Worse
"It's Not Rape If You Enjoyed It": A scene only available in the Korean version of the film (the director cut it out of the international version for pacing reasons) has Kyung-Chul raping his cannibal friend's wife only her for to enjoy it after a while.
Jack Bauer Interrogation Technique: Soo-Hyun uses this on some suspects early on when he's looking for the killer.
Overt Operative: Soo-Hyun
Parental Abandonment: Kyung-Chul has a son whom he left with his parents.
Pay Evil Unto Evil: Soo-Hyun's vow.

I'll promise this. I'll give him pain that's 1,000 times... no, 10,000 times more painful.

The Killer Becomes the Killed
Revenge:
- Revenge Before Reason: What eventually defines Soo-Hyun.
Sacrificial Lamb: Joo-Yun, whose death at the hands of Kyung-Chul kicks off the plot.
Serial Killer: Kyung-Chul.
Serial Killer Killer: Soo-Hyun
Shout-Out: Kyung-Chul ends up in a situation straight from Bloodsucking Freaks: in a guillotine, holding the blade up with his teeth.
Tranquil Fury: Soo-Hyun maintains this state throughout the movie.
Villainous Breakdown: Near the end of the movie Soo-Hyun succeeds in getting Kyung-Chul to beg for his life like so many of his own victims. Subverted in that it was an act on Kyung-Chul's part.
- Then played straight when Soo-hyun leaves and Kyug-Chul's parents and son for earlier come to visit him. Kyung-Chul really starts to panic as they're about to see him in the state Soo-hyon left him in, holding a rope, that released would let the guillotine down, with this teeth.
What Happened to the Mouse?: What happened to the schoolgirl and the kidnapped victim in the cannibal's house? Also, Soo-Hyun's sister-in-law, though Word of God has it that she was killed