Sometimes, a character you care for is going to die. Rather than killed off by the bad guys or some cosmic whim, though, the murderer is another character who cares very much for the deceased. Perhaps your little sis has become a Tragic Monster and needs to be staked, or maybe you have to Fight Your Friend to the death. Occasionally it's a case of Shoot the Dog or Mercy Kill. In any case, the characters know each other, as well as their relationship to each other. And the killer knows that the other has to die for anything to be resolved. In some cases leads to Cradling Your Kill.
In video games, this is invariably a Player Punch. This trope usually doesn't villainize the killer, since the now-dead character generally has to be killed to right wrongs, or at least keep the story going. Doesn't stop him or her from feeling like crap afterwards, though.
May or may not overlap with Self-Made Orphan.
As a Death Trope, several if not ALL Spoilers will be unmarked ahead. Beware.
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Anime and Manga
Neon Genesis Evangelion: Shinji killing his only friend Kaworu, in order to save humanity. Kaworu actually smiles when he tells Shinji he has to die...
Baldr Force EXE: Tohru has to kill Ren to keep her from destroying everything in the Wired.''
Raziel from Angel Sanctuary forces himself to shoot his beloved superior Zaphikel when the latter transforms into a ghoul.
Blood+: due to Psycho Serum Delta 67, the heroine Saya's adoptive father George Miyagusuku starts to turn into a mindless bloodthirsty monster and she must reluctantly kill him before the drug takes effect.
Code Geass: Lelouch (as Zero) is forced to shoot Euphemia after he accidentally Geasses her into killing all the Japanese, sending her on a rampage. Just as he does it, he mentally bids her farewell, and even thinks to himself that she was his first love. He's later shown angsting over it.
And then there's the finale, where Suzaku, disguised as Zero, stabs Lelouch in a Thanatos Gambit. He's shown crying while doing it.
It's also especially tragic because everybody except Lelouch thinks Suzaku is dead and since he was an accomplice in the Zero Approval Gambit, he can't go public or he'll ruin Lelouch's plans. Also, he can't take the easy way out because his "live" Geass forces him to do exactly that.
Weiß Kreuz loves this trope. Loves it. Aya has to kill two of his mentors; Ken has to kill his best friend, girlfriend, surrogate mother, and old friend's brother; and Youji gets to kill three girlfriends.
Sakura has decided to kill Sasuke with her own hands, to save their land and spare him from falling even lower than he already has. Subverted, as when push comes to shove, she can't bring herself to do it and is nearly killed herself.
In the backstory, Itachi did this when he slaughtered the Uchiha Clan, including his own parents whom he killed last, to pre-empt a coup. A flashback shows him about to cut down his parents who aren't even trying to fight back. Just to twist the knife further, they spend their final moments assuring Itachi that they still love him and respect his decision and ask him to look after Sasuke. Itachi is crying the entire time. Speaking of the Uchihas, the Mangekyo Sharingan is unlocked by the death of a loved one ( Kakashi's turned out to be a Suicide by Cop, so it doesn't need to be deliberate).
Kakashi discovers that his hero and childhood friend Obito Uchiha caused the Fourth Shinobi War, which makes killing him Kakashi's responsibility and no-one else's. An interesting example, since Naruto (the idealist) still wants to redeem him, while Kakashi and Minato Namikaze, who knew and loved him, fight only to kill.
Subverted when after Obito is defeated, just as Kakashi is about to kill him, Minato stops him from doing so so that Obito can have a chance at redemption.
In RG Veda, believing that Sōma can't survive the battle and will be killed, Kendappa-ō kills her herself, and then commits suicide because she sees no point in living on without her.
Bleach: Rukia Kuchiki was forced to kill her mentor and first love, Kaien Shiba, when he became possessed by a Hollow.
In the Claymore universe, this sort of thing happens all the time due to the whole I Cannot Self-Terminate thing. The first instance occured in the very first volume when Clare was called upon to Mercy Kill her girlhood friend Elena.
The instance with Raphaela is particulary memorable, tough.
In Corsair, this is a major issue for Canale. His murder of Sesaam, his lover at the time, is the biggest instance but he also feels responsible for his mother's suicide and the general death and destruction that follow him wherever he goes.
In Project ARMS, all of the heroes say, in no uncertain terms, that they won't hesitate to kill Ryo if he's taken over by the Jabberwock. Given that he fears that happening to him, it's actually comforting. At the end of the manga, he remembers this when he has to bring himself to kill Katsumi, who is possessed by Alice. Fortunately, she gets better.
Puella Magi Madoka Magica: Mami during the third timeline of episode ten's "Groundhog Day" Loop hits the Despair Event Horizon upon learning the true nature of Magical Girls after Sayaka turns into a witch and has to be killed. Not wanting the rest of the magical girls to turn like her, Mami kills Kyouko, but before she is able to kill Homura and Madoka before presumably ending her own life, Madoka shoots her. After doing that, poor Madoka collapses in tears, asking the newly released Homura between sobs why did such things have to happen.
An even more tragic example is later in the third timeline. Madoka and Homura manage to destroy Walpurgisnacht, but both are injured, exhausted and in danger of becoming witches. Madoka uses her last Grief Seed to remove the darkness from Homura's Soul Gem in order to spare her from becoming a witch, and Homura returns the favor by tearfully Mercy Killing Madoka before she becomes a witch.
This is the entire point of the Sacrifice of Berserk, as first revealed in the Guardians of Desire arc. By consigning that which you most love to be eaten by demons, the would-be Apostle (or Godhand) cuts himself or herself off from humanity and opens himself or herself to evil. Unlike most of the examples on this page, this act is presented as a monstrous betrayal of everything the person holds dear and a crossing of the Moral Event Horizon, both because of the Cruel And Unusual Deaths often suffered by those who get the Brand put on them and due to the added little detail that anyone sacrificed in the creation of a demon gets his or her soul condemned to Hell for all eternity.
Taimanin Asagi has Asagi doing this to Kyousuke close to the end. He had been turned into a monster, he was lucid at that moment, and she said "I love you" just before breaking his neck and killing him quickly. You would have to have a heart made out of stone not to feel anything over that.
In Mai Hime, Natsuki takes it upon herself to end her best (and for a long time, only) friend Shizuru's rampage, knowing that both of them will die in the process.
Kyo Kara Maoh likes to flirt with this trope. Particularly Conrad and Yozak—they've been best friends for decades, are probably more comfortable with one another than with anyone else in the world, are the only survivors of their Half-Human Hybrid battalion. But in the second episode in which they appear together, Conrad threatens to kill Yozak if he messes with Yuuri again. This scene is so much freakier when you see it again after learning all the background between the characters.
Conrad also throws Yozak off a cliff during his Face-Heel Turn, right after Yozak attacked him while giving a declaration that was basically, 'you're my best friend and my captain and if this is how it's going to be I'll kill you myself.'
And in the weird guest episode with the mountain of betrayal miasma, where everyone except Yuuri became convinced that everyone else had been compromised by the mist of betrayal and become their enemy. Yozak and Conrad had rather a good duel in the snow.
Even more impressive in that episode was when Wolfram became convinced that Yuuri had gone crazy was going to kill him and didn't invoke this trope, just curled up and waited. Power of Love.
When Conrad and Yuuri met in the coliseum it looked like this was going to happen, too, and about ten episodes later it very nearly did.
In Amakusa 1637, two events shattered Naozumi Yatsuka's view of the world. One was the phenomenon that got him and his friends Trapped in the Past. The other was killing the first person in said past who understood him, his young and handsome slave Shirou. Yes, that Shirou.
In Tekkaman Blade, all of the enemy Tekkamen are either D-Boy's family or close friends, including two brothers (one of them his twin) and a sister-in-law.
In For the Man Who Has Everything, Superman has to do this to escape the Black Mercy. In accepting that his wonderful new life is a dream, he causes the dream Krypton to explode just like the real one. Similarly, Batman has to let Joe Chill kill Thomas and Martha Wayne in his dream just as Chill did in life to escape the Mercy.
The ending to Million Dollar Baby. The film's star boxer has suffered a career-ending injury, is paralyzed below the neck, has no hope of recovery beyond being immobile for the rest of her life, and because she is no longer able to pursue her dream of being a boxer, she wants to die, but cannot kill herself due to her injuries. Her manager, who has during the course of the movie become like a father to her, later makes the painful decision to cut off her life support and give her a massive dose of tranquilizers to avert her prolonged suffering.
Averted in Serenity: "bullet in the brainpan squish." Just enough to scare the audience into thinking that was the planned ending. It is easy to imagine the writer pulling that one.
In John Woo's The Killer, the title character has to put a bullet to Sidney Fung, his best friend, in an I Cannot Self-Terminate moment, after he went through serious hell to get the money the Killer needs to have Jenny's eyes fixed to him and got shot by the bad guys.
Subverted in the ending of Pans Labyrinth, when Ofelia has to kill her baby brother to prove herself as a princess of another world. She refuses to do so. Soon, she's killed... and then she's spirited away to her real home anyway.
The Usual Suspects has a sickening version. According to a legend, when Keyser Söze was a small-time gangster, someone once tried to take him down by going after his wife and children. He came home to find them being held hostage, guns and knives being held to them, pleading eyes, etc. Not to be cowed, he killed them all himself, then the shocked hostage-takers, "then their parents, then their parents' friends..."
Jean Grey as the Phoenix kills both Professor X and Scott Summers.
Wolverine is forced to kill Jean to stop her murderous Phoenix alter-ego from destroying everything.
As mentioned in the Literature section, Old Yeller is one of the oldest examples in film. At first there is a Hope Spot tease when Travis pens the dog in a corncrib, hoping he won't turn rabid — he does.
Both the film and book version of Of Mice and Men show two examples. The first is a subversion depicting a man who has to have someone shoot his rabies-infected dog. He laments that he didn't do it himself. It is later invoked when George has to kill Lenny to save him from an angry mob.
Ransom. Corrupt cop Jimmy Shaker seems to care for Maris, his girlfriend and fellow kidnapper. When he kills the two expendable remaining kidnappers to make himself out as a hero cop, she shoots him in turn, clearly expecting him to dispose of her as well. He seems a bit shocked at this before he kills her as well with apparent remorse.
In The Wolfman (2010), the first werewolf kills his wife and son; Lawrence kills his father and almost kills Gwen too.
The end of Old Yeller, where Travis has to Shoot the Dog after Old Yeller has defended the family from a rabid wolf. Unlike the film, Travis knows the dog will inevitably succumb to rabies and shoots him as soon as he sees the dog's injuries.
In Agatha Christie's Nemesis, a young woman who is about to elope is murdered by her guardian because she was loved by her too much.
Also occurs in A Murder Is Announced. One of the victims was killed by someone who loved them, out of fear that she was inadvertently revealing too much about the first murder.
At the climax of Changes Harry has to kill Susan once she fully turns into a Red Court vampire, turning their bloodline curse back against the Red Court and wiping them out.
The tragic climax in "Mastiff", the last book in the Provost's Dog trilogy. The main character's father figure, Tunstall, betrays her and the crown, bribed by a noble title he can use to marry the lady knight he loves. Beka is duty-bound capture him and bring him to justice for his crimes, while Tunstall, on his part, knows he'll only escape if he kills her. In the end, Beka just barely defeats him, he dies of blood-loss and exposure, and his spirit is terribly regretful for what he did.
In AncillaryJustice, the AI of the ship Justice of Torren is made by the emporer to kill Lieutenant Awn, one of his favorite officers. Immediately afterward Justice of Torren rebels, embarking on a quest for revenge that drives the rest of the book.
Live Action TV
In the re-imagined Battlestar Galactica, Colonel Tigh has to poison his wife after she betrays the resistance on New Caprica (which she did to save his life).
NCIS - Ziva kills her brother Ari and is never able to mention him again without visibly stiffening or crying.
In House, Wilson does this when he turns off Amber's life support. For everybody else, though, it was Alas, Poor Scrappy.
In Torchwood: Children of Earth, Jack has to sacrifice his grandson.
Russell T. Davies seems to like this trope. In The Second Coming, Steven Baxter, who also happens to be the son of God, is poisoned by his girlfriend Judith. She does tell him that the food is poisoned, but he finds that she is right, he must die.
Steven Moffat's not letting off with this trope either, playing it heartbreakingly straight with Rory in Doctor Who, who accidentally shoots Amy in an attempt to hold off Auton control of his mind.
In Merlin, Merlin poisons Morgana — who was unaware that she was the vessel of the Knights of Medhir — because he did what he had to do in order to save Camelot, but at the price of killing his friend and someone he cared about. Many fans, while praising the acting of Colin and Katie, did not agree with Merlin's actions. Also a Shoot the Dog moment.
In Nikita, Alex shoots Thom, whom she had feelings for and even kisses him before he dies.
Examples abound in Supernatural, both with the main cast and side characters.
Bobby kills his wife when she's possessed by a demon. Then he kills her again when Death brings her back to life but learns that she's turning into a flesh-eating zombie. Naturally it pains him a great deal.
Bobby: She was the love of my life. How many times do I have to kill her?
This is the background of recurring antagonist Blood Knight Gordon Walker, whose sister was turned into a vampire.
In the season one finale John Winchester ordered Sam to shoot him with the Colt to take the demon out as well. (He didn't.) And a few episodes later John's final direction to Dean was that he 'had to save Sam,' or he 'might have to kill him.'
Sam's mid-Season Two insistence that Dean promise to do just that if Sam goes darkside. Dean promised. He was lying.
Sam's first girlfriend after his episode-one bereavement turns out to be a werewolf who asks him to kill her. Or there's that time Sam nearly strangled Dean to death, or that time Sam shot Dean, or that time Sam was possessed and shot Dean, and possessed and killed him in the Bad Future.
Downplayed in Season Six, with soulless Robo-Sam determined to prevent Dean from restoring his soul. Rogue angel Balthazar informs him that to get his soul to reject reunion with his body he needs to pollute it with a crime such as patricide. Robo-Sam can't feel love, but apparently Sam's regard for Bobby as a surrogate father is enough for murdering him to be 'good enough.'
Plenty of lesser instances, particularly where family members or Love Interests of both recurring and incidental cast turn out to be or turn into monsters.
Buffy to Angel in the season two finale is the obvious one (although he recovered).
And, as evidenced in flashbacks on Angel, Holtz had to kill his daughter after Angelus (or possibly Darla) turned her into a vampire.
Also in Angel, Gunn stakes his sister after she is turned into a vampire.
Played with in Robin Hood. In the finale of season two Guy of Gisborne stabs Marian to death after she reveals her love for Robin Hood. The crime of passion ends with him being guilt-ridden for the rest of the show's duration, and even in his dying moments he doesn't hold out any hope that he'll ever see her again in the afterlife. He also gives his little sister a vial of poison so that she can kill herself, even after she tells him: "you loved me once."
This is the philosophy of Big Bad John Wakefield on Harper's Island. He also tries to make Henry, his son and accomplice in the murders, kill the woman he loves. Henry refuses.
In the 4th season finale of The Mentalist, Lorelei suggests that in order to become his disciple, Jane bring Red John a gift- the dead body of Teresa Lisbon, his close friend and partner. Subverted in that he only pretends to kill her.
In Once Upon a Time Regina has done this three times. The first time was when she killed her father (who is also one of the only people who love her) to get her revenge. The second was when her one true love was brought Back from the Dead (by someone else) and Came Back Wrong, necessitating a Mercy Kill. She really didn't take that well. Finally, Snow White tricks her into unintentionally killing her mother, who is pretty much the last person left that she does love. The end result has left her very broken, very bitter, and very dangerous.
Part of Zhaan's backstory in Farscape is that she killed her lover because he tried to seize power on their homeworld with the help of the Peacekeepers. Subverted with D'Argo who was wrongfully imprisoned for killing his wife (she was actually killed by her own brother.)
Indirect example: Aeryn betrayed her lover to the Peacekeepers; he was arrested for treason. They undoubtedly tortured and killed him, which would not have happened if Aeryn hadn't turned him in.
In the Masters of Horror episode "Imprint", Christopher believes the prostitute Komomo to be the love his life. He ends up accidentally murdering her during his hallucinations.
In Star Trek: The Next Generation, Worf is paralyzed from the waist down and asks Commander Riker, as his friend, to do this for him in a sort of Klingon ritual assisted suicide. Riker refuses on the grounds that under the ritual, it's properly the duty of the eldest son. Unwilling to ask this of Alexander, Worf opts for a dangerous experimental surgery instead.
The Decemberists' Culling of the Fold is, basically, about this. For pretty much no reason. Just because someone's got to do the culling of the fold.
Agamemnon had to kill his daughter Iphigenia so that the Greek fleet could sail...(opinions differ as to whether he actually did the deed.)
Judas in musical Jesus Christ Superstar (the Biblical text itself could be basis for this trope too, depending on how you look at it).
In Richard Wagner's "Ring", Wotan does this to his son Siegmund in Die Walküre and Brünhild to Siegfried in Götterdämmerung, although the actual killing is done by Hunding in the first case, and by Hagen in the second.
Helena in Resident Evil 6, when she's forced to kill her younger sister Deborah who's been infected by the C-virus.
Minerva from Fire Emblem Shadow Dragon wants to be the one to kill her brother Michalis, an enemy of the protagonist's group:
Minerva: (...) Even now, some part of me loves him.
Minerva: ...I love him enough to spare him death on some stranger's sword, do you see? Let him be punished by my hands.
Can be done in Fire Emblem Awakening. Lucina goes to kill the Avatar when she realizes that the Avatar will soon kill Chrom (her father). If the Avatar is Lucina's Mother or Husband, the scene gets very emotional.
This may happen in Mass Effect 3 if you played a male Shepard who romanced Jack in the second game and then didn't do the Grissom Academy sidequest - when you get to the Cerberus base in the endgame, you'll find audio logs of Jack being tortured and then have to fight and kill her after she's been forcibly transformed into a Phantom.
Metal Gear Solid 3. The player, as Naked Snake, is actually forced to press the button and shoot The Boss while she's down.
The end cutscene twists the knife by revealing that The Boss was a Fake Defector after all, and it was her sworn duty to be killed by Snake in order to prevent a nuclear war.
The Boss had to experience something similar: She ended up having to go to Tselinoyarsk in 1962 to fight The Sorrow, and the flashbacks shown when Snake regains consciousness implies that she was unwilling to kill The Sorrow. Peace Walker explains the exact circumstances of what happened: The Philosophers forced them to fight each other to the death under the threat of Ocelot's life if both survive.
You have to do this in Shin Megami Tensei III: Nocturne if you take the Neutral path, in order to stop your friends from bringing their selfish ideas of paradise to reality.
Or, in fact, if you take any other path. You can't be allied to both Chiaki and Isamu after all, you'll have to fight at least one of them.
In Valkyrie Profile: Covenant of the Plume, the titular feather is used to sacrifice party members, but it will only work on people who already trust you as a friend. So they have to like you for you to kill them.
In Riviera: The Promised Land, the trope is zigzagged, with a huge deal made out of how Ein is going to have to fight his mentor and best friend Ledah; the player is made to expect this trope. The battle leaves Ledah badly injured and asking for a Mercy Kill, but Ein refuses on the grounds of no way is he doing that to a friend. Shortly after this, Ledah does die, but it's at the hands of an enemy character after all.
Yggdra Union has quite a lot of these—you are forced to kill the sympathetic queen of the Undines, either Roswell or Rosary (both of whom are otherwise recruitable), and a lot of innocent Bronquian civilians; in each case Yggdra and company are left wondering whether this is really the right thing to do. On top of that, there are three Shoot the Dog fights—against the Verlaine ruler you killed and Kylier after they Came Back Wrong, and Gulcasa, maddened by grief and about to unwittingly trigger The End of the World as We Know It by very literallysacrificing himself. The last three especially are infamous Tear Jerker moments.
Gungnir zigzags the trope much in the same manner as Riviera, but ultimately averts it against all odds: despite the huge, dramatic battle between Julio and Ragnus, Julio doesn't kill his brother at the end of it, and after a lot of yelling at the party, Ragnus gets up and walks away.
It's part of the backstory of four members of the main cast for similar reasons (we play Lloyd and Genis as they're made to kill Marble, Regal killed his lover and Kratos killed his wife.)
The fight with Marble does this weird after the fight, Marble (who looks like a monster, and nothing like her original form) seems to be in much better shape then Lloyd and Genis. The only time she seems to be in any sort of pain is when she struggles to take back control of her body (which is when Lloyd and Genis learn who she is). After saying her goodbyes, she latches onto Forcystus and explodes. Despite Magnius' insistence that they killed her (who at the time is trying to turn Marble's granddaughter against the party, by leaving out details like that fact that Marble was turned into a monster with no control over her body, and therefor is an even less reliable source of information then normal), that might not be the case.
In an alternate route, it's possible to fight and kill Zelos - very close to one member of the cast (who mourns him) and a character many players adore.
Less prominently, Yuan is fighting to prevent the resurrection of his fiancée.
Subverted when Lloyd has to fight his father, who fully intends to die but ends up saved against his will.
The last boss battle is against Mithos in child form and you can have Genis, who befriended him, join in the fight.
And in the sequel, the last two boss battles are Emil VS Richter, in which Emil has always idolized Richter and looks exactly like Richter's dead best friend, then Emil VS his crush Marta and friend Lloyd, which is also a very effective and unexpected Player Punch since Marta was the only other permanent member of your party for the entire game, and Lloyd is the hero of the first game.
In FAMOUS 2's evil ending has Cole do this to Nix and Zeke
Left 4 Dead: In Zoey's backstory, she shot her father so that he would not become infected after being bit. However, It's heavily implied that he was a carrier (immune), but Zoey couldn't have possibly known this...
Imaginary!Barry in Alan Wake's second DLC "The Writer" lampshades this with the line "'kill your darlings'" as Alan goes to the Cabin for the final battle.
Dragon Age II is madly in love with this trope. In the prologue, Aveline is forced to kill Wesley, her husband, to save him from the Darkspawn taint, unless Hawke does it for her. Later on, Anders has the choice between either killing his ex-lover Karl, or leaving him to remain Tranquil, which he and Karl both regard as a Fate Worse Than Death. Hawke may be forced to Mercy Kill a tainted sibling, and Merrill may have to kill her mentor and adoptive mother, Keeper Marethari, as well as potentially her entire clan. Varric ends up having to either Mercy Kill his brother Bartrand, or spend the rest of his life caring for him as he has been driven completely insane by the idol (after Bartrand tried to kill him). Fenris may kill his sister, in revenge for betraying him to his former master. And in the endgame, Hawke may kill his/her lover, if s/he romanced Anders and chooses to kill him after he blows up the Chantry.Damn.
BlazBlue: After her love interest, Lotte Carmine, lost his bodyand his mind and turned into Arakune, LitchiFaye-Ling set out to either cure him of his condition, or put an end to him, should that prove to be an impossible task, though no conclusion has been reached yet. The developers play this for heartwrenching drama in the canon continuty, but aren't shy to play it for laughs everywhere else.
In The Walking Dead, Clementine may do this to Lee to prevent reanimation and as a Mercy Kill before he completely succumbs to the bite.
An even more gut wrenching example is when Duck got bitten by a walker, forcing everyone to kill him before he turns into a walker. Katjaa tries to kill him herself, but couldn't do it and shoot herself. Now you get to choose to let Kenny shoot him, or do it yourself.
At the end of Season 2, Clementine forced to either stop an enraged Kenny from killing Jane by shooting him or look away and let him finish the job.
In one ending of Hyperdimension Neptunia mk2, Nepgear has to kill all the other CPUs and Candidates, or those she can't bring herself to kill do it for her. None of them die quickly. At all. Have fun listening to a couple of children hysterically scream they don't want to die as they slowly expire in excruciating pain.
In War Craft III, at the end of the Human campaign, Arthas becomes a Death Knight and kills his father.
In The World Ends with You Joshua tries to invoke this by telling Neku that if he Shoots him, that he'll give him the job of Composer. Luckily for both of them, Neku refused to do this, and it was just a test
This trope is Survival of the Fittest to a tee. Particularly, in V2, Bryan Calvert has to Mercy Kill his best friend, Seth Mattlock, en route to to fighting Mariavel Varella, a former friend turned psycho.
In the fourth season finale of Archer, Sterling, Lana, Ray, and Cyril are all trapped in an underwater base and have to make a long swim to safety, and there's only three wetsuits. To save the rest of the team, Archer offers to let one of the others drown him, with the expectation that once they reach the escape vehicle, they can revive him. Lana does the honors, and finds it a lot harder than she expected.
Saddam Hussein would order his bodyguards to kill members of their family, so they would "have nowhere to run."
In seppuku, the role of the kaishaku is to behead the man who has just committed the act. It was usually filled by a friend, or at least a loyal servant. This likely formed because seppuku, being a suicide ritual in which you stab yourself in abdomen and cut left from right, would otherwise bring about an incredibly painful end. The exact time to behead varied and was discussed between the principal and kaishaku beforehand - while initially the beheading was performed after stabbing themselves and cutting horizontally, it changed as time went on to that they may beheaded as soon as they stab themselves before they can even show pain from it, or even just showing they intended to go through with it by making a motion toward grabbing the suicide blade.
This is the (incredibly twisted) logic when it comes to some cases of Pater Familicide (or any variant thereof), where the killer does so because they firmly believe that their family is better off dead.
Nazi Propaganda minister Joseph Goebbels and his wife Magda committed suicide in 1945 because it was clear that the war was lost. Before doing so, they let all their six children swallow cyanide pills so they could die too.
Japanese criminal Sade Abe strangled the man she loved to death while having sex. Afterwards she cut of his penis and carried it with her. Her morbid lust story later inspired the film In the Realm of the Senses (1976).
Obsessive stalkers can also cross this territory.
John Lennon was presumably shot by a man who claimed to be his biggest fan.