Hourglass Plot

A Story Arc in which two characters or groups slowly, and involuntarily, swap their positions in life. These positions are usually social (who's high-status, who's popular), economic (who's rich), and most of all, moral—who is decent and who is a ruthless bastard. The swapping often leads to escalation—the new poor person is poorer than the old one was, or the new amoral one is much nastier than the old one was.

The pathos from the Hourglass Plot comes from how neither character learns from the situation—they act just the same to each other as they did before, but with roles reversed. Particularly cruel shows will create an infinite-loop Hourglass Plot, where two hostile characters keep swapping positions and treating each other as badly as ever. In rare cases, such plots will involve the characters barely interacting with each other... a pure comparison of one person's rise to another person's fall.

Lucky characters will get a Not So Different moment and actually learn from it.

Compare: Prince and Pauper, Perspective Reversal, Freaky Friday Flip for an especially literal case, and Perspective Flip for when it's a Retcon instead of a plot development. Compare and contrast: If You Kill Him You Will Be Just Like Him, You Kill It, You Bought It, and Not So Different.

Examples of Hourglass Plot include:

Anime and Manga

Shinji and Asuka go through an Hourglass Plot in the last episodes of Neon Genesis Evangelion. Then several more cycles in the End of Evangelion movie.
In Phoenix: Karma, Gao begins as a ruthless bandit with a Freudian Excuse and Akanemaru is a simple artisan who winds up stabbed by him for no good reason. As the story progresses, Gao finds salvation through art while Akanemaru discovers his own ambition; by the end, both are changed men, and Gao is a sculptor whose talents outshine even Akanemaru's. The petty Akanemaru will not stand to be upstaged by Gao and throws away his own redemption, telling the tale of Gao's origins as the bandit who wounded him; Gao's remaining arm is taken as punishment and he is thrown into exile. However, Akanemaru himself dies in a fire trying to save his work, and as he dies, the Phoenix tells him that he will never be reborn as a human; Gao, on the other hand, manages to return to his art despite his disability.
In Macross Frontier, popular idol singer Sheryl Nome serves as a mentor to up and coming Ranka Lee, but later Sheryl becomes ill and as her popularity wanes, Ranka's soars to the point of becoming a heroine capable of using her song to scare away enemy aliens. Then it happens again when Ranka loses her will to sing and makes a Face Heel Turn while Sheryl takes her place when it turns out she has the same power.

Film

A two-parter in Trading Places. In the first half, Dan Aykroyd and Eddie Murphy swap lifestyles. In the second half, they team up to bankrupt the decadently rich Duke brothers and get rich in the process.
In the film version of The Count of Monte Cristo, after his betrayal of his best friend, Fernand is set up with a beautiful wife and an inherited fortune and noble title, while Dantes is locked away in a prison for 16 years. After his escape and subsequent execution of his plans for revenge, Dantes is now the one with titular noble title, beautiful woman, and nigh-limitless fortune, with Fernand's fortune completely lost, his woman gone, and under threat of imminent arrest for murder and conspiracy.
You may have to squint a bit, but this was part of the Character Development between Neo and Smith in The Matrix and its sequels. Or so the directors say, anyway: Smith picks up human emotions and independent goals (which he doesn't like) while Neo finds himself as a "cog in the machine" with a pre-destined goal (which also proves to be a bit of a drag).
Juno and Mark. She keeps going over to his and Vanessa's house to get to know them better and see what kind of family her baby will have ("I just like being a piece of furniture in your weird life"), while his exposure to her and her teenage flippancy gives him second thoughts about his adulthood and eventually causes him to bail on his wife and the coming baby, to Juno's shock and dismay. His regression triggers her coming of age.
In What About Bob?, Bob Wiley starts off all-but-paralyzed by his various neuroses, while Dr. Leo Marvin is a psychiatrist who's just published a best-selling self-help book. Bob's interactions with the Marvin family helps him overcome his fears and learn to interact with normal society—eventually marrying Leo's sister, becoming a psychiatrist himself, and authoring his own book. Leo, meanwhile, becomes increasingly irritated and unhinged in response to Bob (in part because he feared that Bob was replacing him in his family's affections) and ends up catatonic. Though seeing Bob's and his sister's wedding apparently cures him.
In Primer, Aaron starts off as a family man and rather risk-averse (note the scenes where he worries about needing eye protection and warns his wife against using the first batch of ice from the new fridge). Abe starts off unmarried and rather more devil-may-care. Over the course of the film, access to a Time Travel-powered Reset Button makes Aaron become more aggressive and willing to take risks, and he eventually leaves his family. Abe, on the other hand, becomes increasingly worried about the side-effects of time travel and oddly protective of Aaron's family.
The entire plot of She Devil.
The two divorcees in Woody Allen's Celebrity
In the beginning of Dogma, Loki is portrayed as the more ruthless and reckless, wanting to go on one more divinely righteous killing spree before re-entering heaven, while Bartleby is the one who feels compassion for the humans and is more reserved. However, halfway through Bartleby snaps and becomes an Omnicidal Maniac bent on killing everyone, and it is Loki who is attempting to hold him back.
In the 2011 film One Day, based on the novel by David Nicholls, the two protagonists Emma and Dexter come from completely different backgrounds and life goals, with Emma starting out as a poor waitress after graduating from university and Dexter beginning as a successful television host. Over time, Emma gains success first as a teacher and then as a writer. Dexter goes on a downward spiral and ends up a poor divorcee.

Literature

Notably appears in Thomas Hardy's 1886 novel The Mayor of Casterbridge,, making this Older Than Radio.
The Scarlet Letter features an Hourglass Plot between Hester and Dimmesdale on several levels, especially at the end of the novel.
In William Faulkner's A Light In August, this happens to Lena Grove and Byron Bunch. Not that any Faulkner book is comprehensible the first ten times you read it, but it's there.
Sister Carrie
Severus Snape and James Potter in Harry Potter. In the begining, Snape is the neglected but overall sweet boy who befriends muggle-born Lily Evens. When they go to school, he becomes incredibly bullied by the cruel and arrogant James Potter. Lily's friend spends more and more time retreating into the dark arts to escape his abuse, but becomes indoctrinated by the cause- one day in a fit of embarrassment, he calls Lily a slur because of her parents. Because of it, Snape loses her friendship forever, despite secretly loving her. Meanwhile, James Potter matures and becomes kinder, eventually gaining Lily's hand in marriage.
Used light-heartedly in the A.A. Milne poem "Twice Times". There are two little bears, a bad one and a good one..."And then quite suddenly (just like Us)/One got Better and the Other got Wuss." Milne then reveals that he's using this as an allegory, since he just realized that his son has finally learned all his times tables, while he's getting so old that he can no longer remember where he put anything.
Older Than Steam: In the first part of the novel, Don Quixote is a Daydream Believer Mad Dreamer and Sancho Panza has Simpleminded Wisdom and represents realism. Both are StaticCharacters. At the second part, Sancho is influenced by Don Quixote and becomes more and more of a Daydream Believer, while at the end, Don Quixote will become Bored with Insanity by Sancho’s influence. The relevance is that they maybe were the very first characters in literature to become DynamicCharacters

Live-Action TV

The TV Movie Summertime Switch revolves around a young street punk and a spoiled rich kid both named Freddie Egan. Their identical names cause the former to be sent to a luxurious summer camp for the rich and the latter to a juvenile correctional facility, though obviously the opposite was supposed to happen. Both end up learning something from the whole experience (especially the rich kid).
On Degrassi Junior High and Degrassi High, neurotic, insecure Melanie is best friends with the insensitive Kathleen. Melanie gains confidence while Kathleen loses hers, and Melanie becomes just as insensitive as Kathleen was when they started. Their problems escalate as they get older, so Kathleen is insensitive to Melanie worrying about her body, while Melanie is insensitive to Kathleen becoming an anorexic abuse victim.
- To be fair, Melanie was the one who told a teacher about Kathleen's anorexia, so she could get help, and was also the one who told her she had to leave Scott.
- The fifth season of Degrassi the Next Generation has Emma swapping moral positions with her entire circle of friends and family. They screw up their lives one by one, Emma redeems them all—and then she snaps under the pressure, becoming worse than any of them ever were. The climax is them trying to reason with her, as Emma threatens them and says they have no moral right to criticize her. ("You take advantage of drunk girls. You are the drunk girl...")
Star Trek: Voyager, "Equinox": The Voyager crew comes across their Evil Counterpart: the lost ship Equinox, whose crew are murdering and enslaving their way across the Delta Quadrant. The villainous Equinox captain slowly becomes paralyzed with guilt, just as Janeway becomes just as ruthless as he used to be in her quest to get him.
The Narn and the Centauri in Babylon 5 are caught in an apparently endless cycle of invasion, occupation, liberation and revenge.
- G'Kar starts out as the arrogant jerk seeking power and advancement while Londo is humbled and accepting of his position in life and the lack of any real power. A couple seasons later G'Kar is humbled and powerless while Londo has become one of the most powerful men in the Centauri Empire with the arrogance to match it. By the end of the series they start flipping again though they lose their arrogance for good.
Smallville had this with Lex and Lionel Luthor. At the beginning of the series, Lex was Clark's friend and ally and Lionel was the Magnificent Bastard Trope Namer. Overtime, Lex begins a descent as Lionel redeems himself.
- Arguably, Clark and Lex fit the description, given their destinies. Clark is usually the meaner of the two in the show.
Attempted in the first two seasons of Friends. First Ross pines after Rachel as she dates Paolo. Then Rachel pines after Ross as he dates Julie. How well this works is debatable, given that Julie was a wonderful person and Paolo was a jerk.
In Carnivale Brother Justin is a preacher who slowly turns to the darkside upon the realization that he is The Antichrist, and also suffers from an unfortunate case of Bad Powers, Bad People. Ben, an escaped criminal on the lam from the law, makes a parallel journey as he comes into his own powers as The Messiah.
Supernatural brothers Sam and Dean swap positions on moral limits in season 4 - Sam's demon blood leads him to kill humans for power, whereas he previously was always insisting they avoid "means to an end" sacrifices. Dean, previously a hedonist who expedited the hunt with an apathetic battleax approach, starts setting limits to the point that he'd rather let he and Sam both die rather than be possessed and possibly injure others in a blunt force strategy of the angels.
Buffy the Vampire Slayer features a What Could Have Been example. Originally, it was planned to bring Faith back at the end of Season 6 and have her, The Atoner fight with Evil Willow. As it was, they didn't fight, though Faith still gat an Oh Crap moment where she saw Willow at full power.

Theatre

The play Pacific Overtures has two friends, a samurai and a peasant with knowledge of the west, exchanging places. The samurai, who becomes an ambassador of sorts with the foreign powers as Japan is forcibly opened to trade, becomes increasingly westernized, while his friend, angry at the exploitative actions of the West, becomes a reactionary after being made a samurai. Tragedy ensues.
Shakespeare's Henry IV Part I.
Also Macbeth, which begins with Macbeth as the moral hero being forced into murder by his wickedly ambitious wife and ends with her wracked with guilt as he's turned into a tyrant.
In Shakespeare's Twelfth Night, Antonio saved Sebastian's life after a horrific storm, when they were both mired in a strange country. Antonio grew very close to Sebastian, and even got into a duel in Sebastian's defense. When Antonio was placed under arrest by Orsino, his old rival, he expected that Sebastian would help him out—only for Sebastian to act like he's never met Antonio before. Antonio is heartbroken—but fortunately he had really met Sebastian's Half Identical Twin, and the real Sebastian is perfectly happy to help Antonio once he finds him again.

Video Games

The Legend of Zelda: The Wind Waker features one of these; a rich man and a very poor man both have their daughters kidnapped, and the circumstances surrounding their return swaps them over, including general nastiness.
- That should be general level of nastiness: the one who starts poor stays nasty and unsympathetic after gaining wealth, and the one who starts rich stays likeable after losing his wealth.
Suikoden IV has this with Lazlo and Snowe Vingerhut. The worse off one gets, the higher the other rises. While Lazlo copes with whatever hand he's dealt, Snowe never seems to learn from his mistakes. Eventually, though, he finally makes his Heel Face Turn and actually starts learning from his experiences in retrospect. It just takes nearly the whole game to get him to that point.
Delita and Ramza in Final Fantasy Tactics, who serve as foils to each other throughout most of the game. By the end of the story, Ramza has abandoned his ties to the nobility entirely, while Delita has assumed the highest position of power within the aristocracy.

Western Animation

The plot of Princess Gwenevere and the Jewel Riders episode "Dreamfields." Kale and Gwen are hit with some magic that causes them to hallucinate they've swapped places. It's enough to almost get Kale to Heel Face Turn...but not quite.
This happens in Avatar: The Last Airbender episode aptly named "Crossroads of Destiny" between Aang and Zuko. Aang is The Chosen One who up to that point had successfully fought off The Empire, while Zuko was a banished, disgraced prince abandoned by his father, the Evil Overlord of said empire, after repeatedly failing to capture Aang. The episode finally sees Aang defeated with Zuko's help, and the following episode brings out that Zuko is now accepted as a prince again in his home country with the approval of his father and famed for killing The Hero, while Aang is thought to be dead after having failed to defend the capital of the one country that could fight against The Empire.
On Gargoyles, the three-part "Hunter's Moon" arc has three siblings acting as the current Hunters. Jason, the oldest and leader, hates gargoyles the most; the youngest, Jon, was willing to believe gargoyles other than Demona might be innocent. When it seems like the gargoyles are responsible for Jason's death, however, Jon snaps and turns fully against them; Jason, meanwhile, actually survives and realizes the gargoyles are good. When Jason tried to defend them against Jon, the latter accidentally shoots and paralyzes the former, which he quickly blames on the gargoyles (in a Not So Different moment with Demona).

Jon: What have I--what have they done to you?!