This trope is common both to vendettas and to serial killings. Vastly different motivations aside, the following euphoric calm can be one and the same. All that bided time, all that anticipation and planning, finally pays off. Now able to admire their work, the killer basks in the moment and takes it all in.
Compare Evil Feels Good and Smiting Evil Feels Good, with either of which this may overlap. May lead to This Is Your Brain on Evil if the killer chases this high again. Contrast Laughing Mad, which is Ax-Crazier (though that certainly may follow this trope); Blood Lust and Orgasmic Combat, where the ecstasy is fairly sexual but not necessarily derived from killing; Blood Knight, where the fight is enjoyed as much as (or more than) the kill; and Dissonant Serenity, where the killer is this calm during the struggle. Not to be confused with Tranquil Fury, which wouldn't kill a fly but is no less terrifying. Frequently combined with Blood Is the New Black.
Since the notoriety of more recent real-life killers can deeply affect their victims' loved ones, please be cautious when adding Real-Life examples!
- Death Note. While Light Yagami starts off as a Knight Templar who kills criminals out of an extreme sense of justice, he becomes more corrupt over the course of the story and it becomes increasingly clear he enjoys killing and takes glee in it.
- Heavy Object. Skuld Silent-Third is a Serial Killer who experiences a near sexual pleasure in the act of killing. A glimpse in her mind when she was getting ready to murder showed she was seeing psychedelic colors.
- Tokyo Ghoul is effectively built around this trope, with many of the bad (and on occasion even the good) Ghouls murdering huge amounts of humans for the fun of it. This is one of the more justified examples as Ghouls need to eat human flesh to survive, but on rare occasions, it's this trope played straight.
- Gold Digger: An eventual revelation of the Shun-Leep School of Supernatural Martial Arts (which is used by various heroes) is that it has a series of forbidden techniques called "The Killing Blows" — they are so powerful that are a near-One-Hit Kill Touch of Death (and pretty violent, at that), but the side-effect in the user's body is a heroin-like euphoria that is incredibly addictive, which leads people who use the Killing Blows to eventually become hyper-violent Blood Knight types and even the occasional Serial Killer. This plot point overall is a double-barreled Shout-Out to the Street Fighter Satsu No Hado and Star Wars' Dark Side of the Force (never let it be said that Fred Perry doesn't know how to apply his Reference Overdosed).
- Sin City: According to Patrick Henry Roark, Kevin came to him with guilt over murdering and cannibalizing prostitutes, despite feeling in it "the touch of God Almighty." This led the cardinal to not only cover up his crimes but join him in them as well.
- In The Chronicles of Narnia: The Lion, the Witch, and the Wardrobe, when the eponymous Witch kills the eponymous Lion, she has a brief expression of clear euphoria on her face, complete with closed eyes. It's unclear whether this is typical for her or if it's just due to this one specific kill, but she definitely takes an excessive amount of good feeling from the act.
- O-Ren Ishii during the anime sequence of Kill Bill (see image). Satisfied with the vengeance she got for her parents, she tilts her head back and blissfully sucks in a deep breath. When the late Boss Matsumoto's subordinates arrive on the scene, all she can do at first is flick her narrowed pupils their way in a look of Oh, it's you...
- The Silence of the Lambs: After calmly brutalizing his two new prison guards and billyclubbing the one to death, Dr. Lecter closes his eyes and waves his hand once more to the tune of a Bach variation. His moment of calm self-indulgence ends as the remaining guard's desperate struggle calls him back to reality. Lecter, nonetheless hardly fazed, picks up the dead guard's pocket knife and ambles over to the latter's partner:
Dr. Lecter: "Ready when you are, Sgt. Pembry..."
- Vatta's War: Kylara Vatta discovers, after she kills for the first time in self-defense, that she gets a thrill of victory from doing it something that recurs throughout the series and she considers similar to a drug addiction she has to avoid feeding if possible.
- The Vampire Chronicles: Downplayed when a vampire is feeding on a human while they die. It's described as a "wallop" and a "rolling delirium" for the vampire, but not particularly addictive compared to their obsession with blood itself.
- Invoked in the first vignette of Black Mirror: Black Museum, which features a doctor with a prototype implant that lets him feel the pains of others to help him make better diagnoses. While it worked wonderfully, the implant malfunctioned after he was reading somebody as they expired, causing him to start feeling pain as addictive pleasure (which was explicitly compared to a drug). After habituating, he eventually resorted to torturing a guy to death and had the high of his life and then fell into a coma. In the "present day" of the story, the doctor is still comatose and awaiting trial.
- Dexter: The title Serial-Killer Killer gets a rush out of killing — one of the few emotions he ever feels— and likens it to an addiction, complete with withdrawal symptoms. He's often shown sighing in relief after claiming another victim.
- Doctor Who: In "Spyfall", the Master admits to the Doctor that he gets a buzz in his chest when killing someone for no reason.
- Though Dr. Hannibal Lecter's kills in the Hannibal TV series more often exemplify Dissonant Serenity, some of them — such as of his old colleague Dr. Sutcliffe — show him overtaken by tranquility specifically after his work is done. Then, of course, there's the whole cooking-them-for-himself-and-for-unwitting-guests bit.
- Warhammer 40,000: Inverted with Angron and several of the World Eaters marines, who have cerebral implants known as the Butcher's Nails that cause them to feel pain whenever they aren't killing something.
- The Roguelike Serial Killer features a serial killer whose homicidal urges have to be fulfilled by emptying the bloodlust bar, lest the player became an Omnicidal Maniac.
- In Mass Effect, Ardat-Yakshi, asari with a rare genetic disorder, are considered dangerous because they experience this trope in a very literal way. Asari reproduce by mentally linking with their partner's nervous system to read their DNA and use it to randomize their own. When an Ardat-Yakshi does this, she causes a brain hemorrhage, with the most extreme cases of the condition causing instant death to their partners. The feedback from doing this causes a narcotic effect that proves extremely addictive, and the ones who turn into serial killers leave behind astronomical body counts in their never-ending quest to experience this high as much as possible.
- The Cyclops Killer of AI: The Somnium Files was unable to produce the hormone oxytocin, which rendered him incapable of feeling positive emotions except through killing. He claimed his first victim at the age of twelve. When he undergoes a "Freaky Friday" Flip, he is unable to get the same rush when he murders, so he hunts down the person with his original body.
- In Far Cry 3, Jason claims that he was upset the first time he killed somebody, but that he's gotten so used to it that he's not just no longer bothered—it actually feels very, very good.
- Higurashi: When They Cry:
- Keiichi in the Tatarigoroshi arc recalls no visceral reaction to having finished off Satoko's abusive uncle Teppei. He notes instead a sublime comfort beneath the heavy rain.
- Rena experiences a deep fulfillment in Tsumihoroboshi-hen, having killed the woman who had seduced her father in a "badger game." Of course, Rina/Ritsuko was about to kill her for knowing too much, so it was technically self-defense...though try gauging that from Rena's reaction.
- The mentally unstable King Otto of Bavaria supposedly shot a peasant every morning to keep himself in a good mood for the rest of the day. Or rather, he would shoot a (blank-loaded) gun at a servant dressed in peasant clothes, who dutifully screamed and collapsed to the ground.
- Infamous murderer Karla Faye Tucker claimed that she experienced multiple orgasms as she took a pickaxe to her victims.