The Plot Reaper

Someone's in the way.

A character is more skilled than the hero, more awesome than the hero, has the job that the hero should have, or has the love interest the hero should have (or else is a love interest the hero shouldn't have). They might be the Obstructive Bureaucrat who's keeping the hero from going to the places he or she needs to go to save the world. Maybe they're the symbol of childhood innocence and the main character has to grow up now.

It would take time and characterization to have the hero deal with it, so... the plot removes the complication by killing it. Problem removed, and the plot goes just as planned.

The Doomed Hometown provides both Parental Abandonment and the desire for revenge. Hey, ties to stay home just get in the way of the plot. It's practically in the definition of The Obi-Wan to get killed off, because it wouldn't do for him to defeat the villain. Also, if there's corruption among the human hero's good guy organization, it's...messy to have a civil war or rebellion; especially if the corruption isn't full out Card Carrying Villains. It's much cleaner to have the "real" villains kill them off or convert them fully, and then have the heroes take care of said less nebulous villains.

Death of the Hypotenuse is when this is used as a way of Cleaning Up Romantic Loose Ends. For a nonlethal version, see Deus Exit Machina. Diabolus Ex Machina is when someone dies at the end just for the sake of a tragic ending. See also Too Cool to Live. Stupid Sacrifice occurs when the writers can't be bothered to think of a better way to kill someone off, but don't want to Drop a Bridge On Them. This trope often takes the form of Sudden Sequel Death Syndrome.

And of course he's responsible for Plotline Death.

As a Death Trope, Spoilers ahead may be unmarked. Beware.

Examples of The Plot Reaper include:

Anime and Manga

In the third season of Magical Girl Lyrical Nanoha, it is revealed that there's quite a bit of corruption among the higher-ups in the Time-Space Administration Bureau. This would get very messy if the cast had to pick sides. Nope! The villains kill them all off.
Word of God flat-out admits that this is the reasoning behind the death of Naomi Misaora in Death Note.
Kamina in Tengen Toppa Gurren Lagann has the bad luck to be Too Cool to Live, and thus far more popular than the actual main character, Simon. Thus he gets impaled in the eighth episode. On the plus side, he does get a city named after him post-Time Skip.
Whitebeard from One Piece. Of course it is inevitable as the character's existence is standing in the way of not only the main character's ambitions but 70% of the extended casts' hopes and dreams too. That's what happens when you're the most likely candidate for the title the hero wants, and you're not evil enough for him to beat you himself.
- By merit of being his successor, Ace fell from this shortly before.
- This was also done to make the Evil Counterpart of the hero even more powerful and start a new age of piracy.
Even aside from the standard Mentor Occupational Hazard, if Teresa from Claymore hadn't died, Clare would still have had a mother figure and would never have become a Claymore. Also, the main villain would have been curb-stomped before ever reaching her full potential. And Teresa turning into an Awakened Being would completely shred existing characterization. She never had a chance.
In Naruto Konan was disposed of after her Heel Face Turn and the death of Nagato/Pain, to whom she had been most loyal, with her killer motivated partly to punish her for her betrayal and partly to obtain the Rinnegan she was protecting.
In Highschool of the Dead, Hisashi gets taken out early on so Takashi can take the reigns as the protagonist and win the female love interest's affections.

Comic Books

This is ridiculously common in comic books, but the most egregious is probably the New X-Men. At the end of House of M, when 90% of Earth's mutants lost their powers, the depowered students at Xavier's were Put on a Bus home for their safety (even though many of the kids had nowhere else to go). And then the bus was blown up by Reverend Stryker. One could argue that the death of all those students at once, coupled with the book's already-high mortality rate, was simply because the writers didn't know what to do with all those students.
- Because, you know, putting them on a bus to go home and lead uneventful (or eventful but not eventful enough to be in comics) lives and maybe come back later repowered or seeking revenge or as supporting characters or not coming back ever, well that sort of thing just wouldn't do for an X-Book.
- Also, this sums up how Jean Grey inexplicably dies at the end of Grant Morrison's X-Men run. An editorial proclamation was made from on high to get rid of her in order to make Cyclops "more interesting" by having him date Emma Frost.
While writing Watchmen, Alan Moore intended for Rorschach to live. After working on the character for a while, though, he realized that letting him live would create a whole other set of issues, or would require everything after the climax to be one big Out-of-Character Moment. Thus, the character had to die.

Films -- Live-Action

Star Wars - Luke Skywalker's aunt and uncle who only existed to die. They didn't want him to leave the farm; they had to be removed. Particularly obvious when Luke, who is completely obsessed with a father he never knew, never once mentioned the couple who raised him from infancy ever again.
Two variations of this trope were considered for Casablanca, both dismissed: Victor dying and Rick dying.
The Plot Reaper claims the Chinese man who owned Gizmo early on in Gremlins 2 so that Gizmo will end up being reunited with the protagonists.
Did you think big, bad, giant tentacled monsters capable of sinking ships are safe from the Plot Reaper? Well, you thought wrong. The Kraken, which was a major menace in Pirates of the Caribbean: Dead Man's Chest, shows up in the next film dead on the shore. Apparently, Cutler Beckett forced Davy Jones to kill the Kraken off-screen. His death is used to illustrate the end of an era—on par with one theme of the film, particularly the scene the reveals the Kraken's corpse—but perhaps the film-makers also felt the Kraken stood in the way of the story at this point, and giving it a big climatic last battle would have made the movie at least a half hour longer.
- On a related note, the screenwriters have remarked that the third movie would've been much easier to write if, at the beginning, a whole bunch of characters got hit by a bus.
In The Bourne Supremacy, Marie dies almost immediately because there's no way Jason Bourne would have continued with the plot otherwise.

Literature

In the last three Harry Potter books, damn near EVERY older male Harry has come to rely on, or could ask advice of, gets offed. It starts with his father, then Sirius, then Dumbledore, "Mad-Eye" Moody, Remus Lupin. It's dangerous to mentor The Boy Who Lived. The exceptions, however, are Arthur Weasley, who makes it through the last battle relatively unscathed (but Arthur Weasley surviving caused Rowling to kill Tonks -- she was in Lupin's blast radius), and the other exception is Rubeus Hagrid, because around Book 5 it became Harry and friends' job to parent Hagrid, rather than the other way around.
In Lois McMaster Bujold's novel Komarr, Ekaterin's unlikeable, abusive, and all-around Jerkass of a husband dies just as she has decided to leave him, freeing her to be courted by Miles Vorkosigan. Unfortunately, he dies in such a way that fewer than a score of people in the Barrayaran Empire have a high enough security clearance to be able to satisfy themselves that Miles didn't kill him out of jealousy. Which causes problems for Miles all throughout the next book...
In Garth Nix's Old Kingdom trilogy, it is pretty clear from the beginning that Sabriel's father Terciel is on the verge of Death, and not just in his line of work, but that considering how long he's spent in Death, and the fact that all the signs point to Sabriel inheriting the title of Abhorsen, he is granted, as he himself says, only "a hundred hundred heartbeats" left in life.
Leino in Harry Turtledove's Darkness series. When his wife Pekka and Fernao, both major characters from the beginning, finally meet at the series' halfway point, they slowly start to fall in love with each other due to both Pekka and Leino kept in total isolation with their colleagues working on top secret projects. Meanwhile, Leino's shagging one of his coworkers (who aside from her looks really has nothing going for her) with far fewer reservations. This could have created a very complicated and messy situation when everyone met, but instead Turtledove kills Leino and his lover at the beginning of the last book. Somewhat played with as news of Leino's death (but not his affair, no one ever finds out about that) initially makes Pekka feel enormously guilty and break off her relationship with Fernao, though eventually they get back together and get married.
- Also, in Turtledove's Worldwar series, A-bomb scientist Jens Larssen is lost and presumed dead after The Race attacks Chicago. When Larssen finally catches up the group that escaped and fled west, his wife is remarried to (and pregnant by) Sam Yeager, a conscripted Army sergeant. What might have been a long, awkward, painful process of working things out between the three of them is sorted in short order by Jens going Ax Crazy, trying to defect to The Lizards, and getting cut down by Rance Auebach's squad before he could turn over the info he had on America's atomic bomb project.
Ygritte from A Song of Ice and Fire. She exists solely to be sacrificed at the altar of Jon's woobiedom.
At some point, Tom Clancy decided that his star character Jack Ryan needed to become President of the United States, despite being completely unelectable in the sense of having no political experience to speak of. The solution: have Ryan nominated Vice President as a political gift to replace an ousted Strawman Liberal VP, then kill off the President, most of the Cabinet, most of Congress, the Joint Chiefs of Staff, and the Supreme Court in one massive catastrophe. What's amazing is that he pulls it off reasonably straight.
- Which led to it being Harsher in Hindsight when 9/11 happened. Much literal turning of Holy Shit Quotient to 11, jumping up and down the sofa screaming "That came right out of a Tom Clancy novel!" Hijacking of airliner etc etc etc... and we all know how it ended. I always wondered if bin Laden was a fan of Tom Clancy...
Edgar Rice Burroughs was in love with this trope. He slaughtered rival love interests, partially reformed villains, and other characters whose continued existence would inconvenience his heroes, with gleeful abandon.
In Charles Dickens' David Copperfield, our hero's first wife (totally unsuitable) has to die so that he can marry his second wife (totally perfect).
- Dickens also brings out the reaper in Bleak House, doing in Lady Dedlock because she cannot remain alive (thanks to Victorian Moral Guardians) once the truth of Esther's parentage comes out.
Attis Aquitaine in the last book of the Codex Alera series. It sure is convenient for the main character that he died, and he was smart and ruthless enough that his survival could have gone either way, and by the end he might not even have needed Redemption Equals Death. However, after the final battle, any denouement where the protagonists have to worry about Aquitaine would be anticlimactic.
- It helps that the character's death wasn't sudden or out of nowhere. He sustains an injury early in the final book that is explicitly described as being sure to kill him slowly and painfully, letting him linger around to affect the plot but setting up his eventual death long before it happens.
Kate Chopin, an otherwise respected author whose work is often used as School Study Media, had a terrible habit of killing off characters she couldn't write a proper ending for. Typically, the character thus slain was someone who'd violated the social order and who was about to get metaphorically reamed by the hatred of their community, but at least once she used a convenient flood for Cleaning Up Romantic Loose Ends.
The Horatio Hornblower series. Maria, the plain and dull woman Hornblower married out of pity and gratitude, dies in childbirth so Hornblower can marry the beautiful and intelligent Lady Barbara Wellesley.
In Gustav Flaubert's novel Madame Bovary, Charles Bovary's ugly original wife conveniently dies, making room for Emma to enter the plot fully.

Live-Action TV

All My Children wrote itself into a situation in which Tad, a biological father who never gave up his rights, is seeking his daughter Kathy, who was unknowingly adopted by Julia. This could have led to a nasty custody battle, in which many viewers would side with Julia, even though we're "supposed" to side with Tad. So instead they just killed Julia off. Problem solved.
Hi, Agent Scott! Bye, Agent Scott!
Colonel Sumner is killed off in the pilot of Stargate Atlantis simply to justify a lower ranking military officer such as Major Sheperd getting command of the entire base.
- One could also include the Icarus planet in the pilot of Stargate Universe. If it hadn't blown up, they could just keep sending supplies.
Admiral Cain, a higher-in-command in the reimagined Battlestar Galactica succumbs to the plot reaper, because she is a hazard and generally unpleasant for the fleet. Asininely enough, the characters actually discuss having her mutinously assassinated (which wouldn't be this trope), but then a toaster conveniently pops her off as to avoid the guilt and implications of murdering your superiors. Hooray for the guilt-free resolution(!)
Horatio Hornblower's best friend for two series, Archie Kennedy, is in the way both of his character development as an isolated individual, and the story itself, as he was not in the books. Instead of having him transferred to another ship, he was written out in a way that would make a return impossible.
The brand-new Chief of Police Tommy Delk in Season 7 of The Closer. He was going to demote a major character to the traffic department and make a character Brenda couldn't stand her direct superior; he was doomed as soon as the audience found that out.
At the end of the Law and Order Special Victims Unit Season 16 episode 'Undercover Mother', Olivia Benson discovers that the human trafficker (and kidnapper and rapist) Johnny D. is the biological father of her adopted son Noah. She angsts for a while about the possibility of this criminal being granted the right to visit his biological son, but several episodes later, in the season finale, Johnny D. is killed off, having committed Suicide by Cop in a confrontation with Detective Nick Amaro (which Johnny D. provoked in an escape attempt he knew he wouldn't survive).
In Season 8 of Game of Thrones, Jorah Mormont dies heroically defending Daenerys Targaryen during the battle against the Army of the Dead at Winterfell. This makes him incapable of preventing Daenerys' later destructive rampage against King's Landing, or being the one to hold Daenerys accountable after the fact (that latter duty ends up falling to Jon Snow).
- Petyr 'Littlefinger' Baelish, the Manipulative Bastard whose schemes triggered the feud between the Lannisters and the Starks in the first place, meets his end at the end of Season 7 so that the Starks won't have to worry about him and his self-serving schemes in Season 8, where they have the White Walkers, the arrival and alliance with Daenerys Targaryen, and the war with Cersei to deal with.
Happens to Logan in the finale of Hulu's Season 4 of Veronica Mars, (as a result of a bomb left over from the season's Big Bad) as creator Rob Thomas felt that if the show were to continue, it needed to evolve into more of a mystery/PI show and abandon the Teen Drama elements from the high school era (which the show had already moved away from). He felt that his lead couldn't have a boyfriend, as in the fourth season he was already struggling with how to get Logan involved in the storyline and felt it would feel phony to keep doing so.

Videogames

Happens to Liberty Prime in Fallout 3: Broken Steel, care of a precision nuclear strike from an orbital weapons platform. If it hadn't happened, the otherwise invulnerable robot would curb stomp the everything in the Wasteland with virtually no effort.
Aeris/Aerith Gainsborough. The Last Of Her Kind, with an obscene amount of magical power, who can talk to the planet and find out everything that needs to be found out, though she can't understand it that well at first. A visit to the ancestral temple of her people later, and she comes into her full heritage, just as the party becomes cognizant of the actual threat to the world. An interesting case in that she actually goes off on her own to resolve the problem single-handedly...with predictable results.
Nihlus Kryik dies ten minutes into the first Mass Effect. Why? He was already a Spectre and was going to be observing Shepard on several missions before making his recommendations to the Council on whether or not to make Shepard one. Nihlus' death (along with the attack on Eden Prime) catapulted Shepard into the ranks of the Spectres and kick-started the game's plot.
Asch The Bloody's fate in Tales of the Abyss since in the end, There Can Be Only One Luke fon Fabre.

Webcomics

In Order of the Stick, Vaarsuvius acts as the plot reaper him/herself by quickly killing the villain Kubota after his capture, stating that s/he really doesn't have the patience to deal with what s/he sums up as potential Filler.
- This one act served quadruple duty: firstly ridding us of the villain in a most fitting matter; secondly avoiding more details that keep us from getting back to the main plot; thirdly acting as Vaarsuvius's Jumping Off the Slippery Slope moment; and fourthly cementing Elan's realization that, while a happy ending is assured for him, those around him—even his friends—are not so guaranteed. So, much like Cael'anon from Looking for Group, he's learning that the world around him isn't as idealistic as he once believed... and it may be a while before we see the end result of this realization.
In Gold Coin Comics, Lance's ties to his past are cut because of a fire so that he may continue with the plot.
In Homestuck, the villian Jack Noir winds up becoming part god dog, and Tavros can control animals with his mind. Since Tavros was seen controlling the god dog that Jack Noir's new form is based on, Tavros could potentially mind control the main villain and end the plot. Obviously, he gets killed due to Vriska.
- This also happens to Jade. Since Jack Noir is pacified whenever next to her due to the god dog's loyalty, Jade winds up getting killed by the Courtyard Droll. However, it's a Subversion, as Jack Noir winds up setting up her revival before getting out of there and avoiding being trapped in another metaphorical leash.

Western Animation

An entire episode of Frisky Dingo is spent setting up Nearl, Xander Crews' identical twin brother. After an extended monologue in which Nearl explains his life history and various motivations, Xtacle Ronny stands up and simply shoots him in the head. "This plot is complicated enough without all this evil-twin bullshit having."