"Wanting connections, we found connections — always, everywhere, and between everything. The world exploded in a whirling network of kinships, where everything pointed to everything else, everything explained everything else..."
— Umberto Eco, Foucault's Pendulum
Say one day you meet a girl and fall in love. Nothing wrong with that. However, on your wedding day, when you meet her father, you remember that he's the guy who failed you in biology in the twelfth grade. Okay, odd, but not inconceivable. But wait, isn't her mother the one who sat next to you at a bus station five years ago and gave you great life advice? And her cousin looks familiar, too. Hold on, it seems you've met her entire family at one point or another throughout your entire life.
And then she comes up to you and reveals that she's met your whole family before as well. In fact, you are her father's brother's nephew's cousin's former roommate. It seems there's only One Degree of Separation.
This is where every character is tangentially connected to almost every other character. It doesn't matter if it's an Easter Egg or important to the Myth Arc. Everyone's connected. This concept as applied to actors is discussed on the page Six Degrees Of Kevin Bacon.
Often part of a Jigsaw Puzzle Plot or a Hyperlink Story. Sometimes just a lot of Contrived Coincidence. See also Generation Xerox. Gets much more complicated when you have Loads and Loads of Characters who all seem to know each other. Or if they don't they quickly do thanks to You ALL Share My Story. Can be seriously aggravated by the presence of Immortals, also prevalent in Generation Xerox
The anime Code Geass, about a disowned prince rebelling against an empire, despite its incredibly large cast, features a great degree of connectedness. The protagonist, Lelouch, has more half siblings than he can count (since his father is an emperor with 108 wives), at least five of which are important to the plot. His father is the primary villain of the series. He and his sister spent time, as children, in the Kururugi household, giving him a personal relationship with his rival, an important businessman, a legendary general, and a girl who will later become an enthusiastic fan of his alter ego. The president of the student council at his school is from a noble family that were supporters of his mother. A military officer he disgraces turns out to have formerly been a guard at his mansion. A Japanese citizen who becomes an important supporter of his rebellion turns out to have been his maid, and also a ninja.
One of Lelouch's subordinates was romantically involved with an enemy knight, who just happened to be the first person to survive Lelouch's Mind Control powers in the beginning of the series, and the enemy knight had amnesia for a while after being shot by a high school girl who had a huge crush on Lelouch. His head scientist was a former colleague of an influential enemy scientist, who is both the mentor to Lelouch's aforementioned rival, and the fiancé of the head of the student council. Lelouch's primary accomplice and confidante was formerly the head of a cult whose members are now supporting the evil empire, and had watched over Lelouch when he was a child. Recently, a powerful knight in the empire was revealed to have had some sort of past connection with Lelouch. Also, a new rival of Lelouch's is a general in the Chinese Federation, who has pledged his life to support a child Empress whose first and only friend is the aforementioned fangirl of Lelouch's alter-ego.
Still, Code Geass isn't really any worse than any other series. The half-sibling thing is important to the plot of the first season, but it's not like their relationship is a coincidence. The rivalry between Lelouch and Suzaku's alter egos and their relationship several years beforehand is also pretty intentional, but closer. The real web of relations come towards the end, when we find out that several characters were in the home of, around, or had some business with Lelouch's mother.
Gundam SEED: In the first episode, Kira finds himself opposing Athrun, his best friend from the colonies. But before that, he runs into an unknown girl who later joins the crew of the Archangel — Cagalli. And she turns out to be his sister. Later on, the Archangel comes across an escape pod from a destroyed ZAFT vessel, containing none other than Lacus Clyne, Athrun's fiancee. By the end of the first season, Gundam SEED Destinybe damned, Kira is romantically attached to Lacus, and Athrun to Cagalli. And their Ace Pilot, Mwu la Fllaga, has an ongoing feud with Athrun's commanding officer, Rau le Creuset, who turns out to be Mwu's father's clone. And the guy who ran the project? The one who eventually genetically modified Kira to be the Ultimate Coordinator.
Some even theorize that the guy who ran the project (and is thus Kira and Cagalli's dad), Dr. Hibiki, may have used Al da Flaga's DNA in the Ultimate Coordinator project, adding yet another attachment.
It seems that in ef - a fairy tale of the two., everyone is tied to each other through their past and present. Episode 10 of a tale of melodies best emphasizes this, as nearly the entire cast comes up in name or on screen.
Almost all of the main characters in Chrono Crusade are connected to Chrono in some way, and through him to each other. Chrono met Rosette and her brother, Joshua, when they woke him up from a long sleep in a tomb. Joshua was then kidnapped by Aion, Chrono's former friend. Chrono and Rosette join the Magdalan Order to try to find Joshua based on advice from Father Remington, a man who was trying to convince Joshua to join the Order because of his powers. Remington was also Mary Magdalene's guard in the Order when Chrono kidnapped her back in 1870. The Elder was her foster father of sorts. During their search for Joshua, Chrono and Rosette run into Azmaria, who has powers startlingly similar to Joshua because they're both Apostles. They all start to look for Joshua together, and run into a "jewel witch" named Satella. Satella is searching for a missing family member, and finds out that her sister, Florette, has become Fiore, Joshua's maid and a servant of Aion. Pretty much the only characters that don't have a strong connection to Chrono, Rosette or Aion are Sister Kate (Rosette's commander in the Order) and Father Gilliam, an ally of Chrono and Rosette's in the order.
In Bakuman。, most of the characters have heard of Nobuhiro "Taro Kawaguchi" Mashiro, the mangaka uncle of the main character and some of the editors have worked with him (Editor in Chief Sasaki, for example, was the one who told him Shonen Jump wouldn't renew his contract). In a later arc of the series, Azuma, an out-of-work mangaka, happens to be Nobuhiro's assistant. Outside of the manga industry, Kaya's father was friends with Nobuhiro in school, and the woman Nobuhiro loved happens to be the mother of the girl Moritaka loves.
Paranoia Agent has this for the first few of Shonen Bat's victims. The copycat victim Shougo is running against the third victim (Yuuichi) for student council president. Yuuichi is being tutored by the fourth victim (Harumi), who has an alter ego Maria that works as a prostitute, and one of her clients is the second copycat victim Hirukawa. Hirukawa's daughter Taeka is the fifth victim.
All over the place in Dennou Coil. The grandfather of protaganist Okonogi Yuko "Yasako" was the doctor of Asazawa Yuko "Isako" and also created the Dennou Coil and 4-4-2-3based off Isako's brother, which gave Yasako and Isako their nicknames. Yasako's grandmother Megabaa (wife of said grandfather) set up the Coil Detective Agency whose membership includes that of Yasako's father (Megabaa's son), who also works for the Megamass Corp. and is the boss of fellow Agency member Tamako, whose immediate superior is Agency member Nekome and is the aunt of Agency member Haraken, who was friends with Kanna, who died in a car accident partly because of Isako's "encoding", who copied her techniques from former "encoder" Tamako who is now trying to stop Isako's "encoding" along with Nekome, who is actually a Double Agent and is really Isako's partner in crime and whose brother Takeru became friends with Yasako.
In Ichinensei Ni Nacchattara, the main character Iori just happens to have his life saved by the sister of his oblivious crush, at the cost of being turned into a seven-year-oldgirl, which causes him to be sent to the same school as the kid whom he risked his life to save. By pure coincidence, his younger sister attends that school as well. He winds up living with his crush (who happens to bear a strong resemblance to the woman Iori's father cheated on his mother with) and her sister, and after their house blows up his real family takes them in out of the goodness of their hearts, still completely oblivious to Iori's true identity. Also, a minor character that Iori and his friends encountered once lives in the same apartment complex.
The Black Jack anime suffers from this. Kumiko is the daughter of Jack's mentor Dr. Honma, and she works for a man named Tetsu who was a pickpocket until he lost his fingers and then had them sewn back on by Jack. In the manga none of these characters are related.
Durarara!!: Everyone—no, really, everyone—knows Mikado somehow. Leader of the Yellow Scarves? his best friend. The Demon Sword and chat room troll Saika? possesses the girl he has a crush on. Urban legend Dullahan on a motorcycle? one of his chat room friends; the other is OriharaIzaya. And Harima Mika, the girl made to look like Celty's head, sits behind him in class.
Nearly every main character in One Piece has a connection to others.
There is a part of Sin City where almost every protagonist is in a strip club, dancing or watching the dancing.
Which is more of a Continuity Nod, since the same scene is shown from different character viewpoints in different stories where they all happen to converge on this one time and place in Kadie's Bar. Sin City is full of similar scenes connecting two or more stories at the same time/place but different perspectives.
Marvel's recent Ultimate Origins mini series appears to be their attempt at doing this for the Ultimate Marvel Universe.
Of course in this case it makes no logical sense whatsoever. For example: Hulk is revealed to have killed Peter Parker's parents even though canonically Spiderman was already a superhero in the UMU when Banner became the Hulk.
Quite frankly, anything and everything Bendis established in Ultimate Marvel Team-Up was either retconned away or blatantly ignored almost as soon as the series was published. Even Bendis himself pretty much ignored everything.
Jenny Sparks from The Authority was the spirit of the 20th Century, and as a result is somehow connected to every mover and shaker of the century, both good and bad — from being raised by Einstein to persuading Hitler to give up painting, and met or worked with pretty much every superhero on the planet. Her successor, Jenny Quantum, will presumably be the same for the 21st century.
Seems to happen to most of the mortal side characters in The Sandman, even excluding circumstances directly caused by Morpheus' influence.
Weightless: Shepard used to live in an orphanage where the nephew of one of the caretaker was Kaidan, then she was bailed out from there by Ghost/ Kai Leng. Later, after her rape, she was rescued by Nihlus, who then was spared by Samara because without him Shepard would die. And now, apparently, Jack looked familiar to her, too.
In Saw, two apparent strangers, Adam and Dr. Lawrence Gordon, are trapped in a room together. It turns out, however, that Adam was hired by a detective to spy on Gordon, who was suspected of being Jigsaw who turned out to be a patient of Gordon's with terminal cancer; this was all part of the plan, but the characters didn't know that when they found out.
Later sequels show that most people that had been trapped by Jigsaw were going to the clinic of Jigsaw's (ex)wife or people he knew beforehand.
The View Askewniverse, often with Jay and Silent Bob being in the center of the Venn Diagram of character connections. Jay and Silent Bob Strike Back is built off of all the characters from the previous films.
Star Wars. Not only is the Evil Overlord whom the main character met through a long series of coincidences his father, but the woman that he happened to meet through the same series of events is his sister. The prequels exacerbate it by introducing a pitiless onslaught of Already Met Everyone;
R2-D2 was owned by Queen Amidala and C-3PO was built by Anakin Skywalker. Boba Fett, as well, is the clone-son of Jango Fett, who is the original model for the entire Clone Army. Chewbacca knew Yoda from the Battle of Kashyyyk near the end of the Clone Wars.
Also, in The Empire Strikes Back, Darth Vader and Boba Fett share a brief exchange ("No disintegration." "As you wish.") In Attack of the Clones, Mace Windu kills Jango Fett while rescuing Anakin Skywalker, along with Obi-Wan and Padme, and then in Revenge of the Sith, Anakin kills (or assists in killing) Mace. So, Boba's dad died because of Vader, but Vader then killed the man who killed his father.
One review mentioned Vader's saying "I sense something..." when he first encounters the Millennium Falcon. No kidding: his son, his mentor, the droid he built and another from his past are aboard. He'd really be losing his touch with the Force if he couldn't pick up on all that.
At one point, there were plans to include Han Solo in the prequels, but they were scrapped when they noticed this trope.
In the original trilogy, there's no reason to assume Yoda and Chewbacca even know of each other, but Episode III implies them to be good friends.
The 1989 Batman movie decided that having The Joker threatening everyone in Gotham City wasn't enough of a reason for Batman to hate him, so it turns out that he was the one who killed Bruce Wayne's parents.
To be exact, Jamie and Sarah are friends of Juliet and Peter, appearing at their wedding. During their reception, Colin has several failed attempts to flirt with women, including Mia. Peter's best man is Mark who knows Mia. Mia is the new secretary for Harry who is married to Karen. Sarah also works for Harry. Karen is the sister of the new Prime Minister David and is also close friends with Daniel. Daniel's son goes to the same school as Natalie's cousins. We also find out that Mia is neighbors with Natalie's family. Even the salesman Rufus, who had earlier wrapped a gift for Harry, manages to help out Daniel and his son at the airport.
The only one that doesn't directly interact with the others is Billy and his manager. However his antics and his music video inspires Daniel's son on how to get his crush's attention.
In Playing By Heart, this is The Reveal — except for some Arc Words, there's no hint of any connections other than the obvious ones, until the end.
Auf der anderen Seite/The Edge of Heaven by Fatih Akin did this with three parent/child pairs. All six characters were connected in some way.
Parodied in a scene in Hot Shots!, where it turns out everyone in the barracks is related in some way.
Also parodied in the sequel (as a type of sequelitis). Topper is sent on a special mission to Iraq where his contact happens to be his former love interest Ramada (who was a psychologist in the previous movie) and one of the prisoners they're there to save is her husband. Also, while Topper's new love interest being on the mission doesn't fit this trope as this is how they met, her having been Ramada's college roommate does.
Also parodied in the revealed background between Saddam Hussein and President Benson. Given Benson's military background and involvement in the Iraq operation of the previous movie, its not inconceivable that they could have met, but when they whipped out lightsabers and began dueling, theres no doubt they were parodying this trope again.
Les Misérables. Would you believe it, Cosette, we just happened upon the same convent of which I had saved the gardener's life? And your boyfriend, what a coincidence, feels obliged to fulfill a debt owed to the same family that abused and starved you for three years! And that same family produced that gamin on the streets who's taking care of his brothers who were supposed to go live with your boyfriend's grandfather and mon dieu let's talk about the Parisian sewers.
And then the barricades, where every surviving character fit for battle (and a few who aren't, like Valjean (seventy-two going on eighty) and Eponine (starving, lovesick, homeless and female)) shows up either during the battle or in the sewers.
The Niven & Pournelle novels Lucifer's Hammer & Footfall. The later one was particularly egregious in this regard. Justified in Niven, Pournelle, & Flynn's Fallen Angels as many of the characters are connected through science fiction fandom.
The Wheel of Time books: Elayne and Gawyn are introduced as siblings, Galad as their half-brother. Whose father, Taringail Damodred, is a relative of Moiraine Damodred (whose cousin, Caraline Damodred, also appears in the series). Galad's mother, Tigraine Mantear, on the other hand, is also the mother of the main character, Rand al'Thor. Meanwhile, the mother of Elayne and Gawyn had an affair with Thom Merrilin, her court-bard-turned-wandering-gleeman, who likely killed Taringail. Gawyn is now (sort of) romantically involved with Egwene al'Vere, who was Rand's love interest back in the first three books, while Rand is now involved with Elayne.
That's just scratching the surface. In this series, They All Share The Story. The mariner Bayle Domon, for example, helped Rand and Mat escape monsters in book one, helped Elayne and Nynaeve hunt the Black Ajah in book four, and traveled with Mat in books eight through 12 or so. None of their meetings were planned, and were barely even voluntary. The Mole who threatened Moiraine in book two also spied on Elayne and Nynaeve in later books. Verin mentored Elayne, Nynaeve, Egwene, Mat, Perrin and Rand, but each in different ways and for different reasons. Character histories like that are completely typical in this series.
Happens in Incarnations of Immortality, by the end of the series. Greatly assisted by the presence of several "temporary immortals" (the longest-lived being Parry) and a literal Fate playing a centuries-long chess game against the Devil. Niobe (Lachesis, the middle Aspect of the incarnation of Fate, formerly Clotho (another Aspect)) is the mother of Orb (Gaia, Incarnation of Nature, from Niobe's second marriage) who's married to Parry (Satan, Incarnation of Evil). Orb's child with Mym (Mars, Incarnation of War), is Orlene (God(dess), Incarnation of Good). Orlene once dated Norton (Chronos, Incarnation of Time), and bore a child (who later died). Niobe's granddaughter, Luna (via Niobe's son from her first marriage), is dating Zane (Thanatos, Incarnation of Death). Kerena (Nox, Incarnation of Night) is a distant ancestor of Orlene's dead husband, and accidentally introduced into her line the curse that would kill Orlene's child. Parry's demon ex-lover, Lilith, is a concubine of Mym. Another Aspect of Fate, Nicolai (Atropos), is a friend of Orb and helped find an adoptive family for Orlene. There's also a very strong hint on the first page of Under a Velvet Cloak that Kerena's sister Katherine is a distant ancestor of Niobe, thus also of Orb, Luna, and Orlene.
The focus of Dirk Gently's Holistic Detective Agency, hence the "holistic" in the title — everyone is connected through the main character Richard. Which only goes to prove that Dirk's ideas about the interconnectedness of all things are not crackpot theories, despite the cynical use he makes of them.
Near the beginning of The Hitchhiker's Guide to the Galaxy, Ford and Arthur end up on the Heart of Gold and meet Trillian and Zaphod. Despite being, respectively, the only three survivors of the Earth's vaporization and the President of the Galaxy, they all know each other already: Ford and Zaphod are old friends from the same star system, Trillian (originally Trisha) recently dumped Arthur for Zaphod at a party, and Ford knew about Trillian through Arthur.
Zaphod: Is this going to happen every time we use the Improbability Drive?
Trillian: Very probably, I'm afraid.
Every single case of The Hardy Boys would somehow turn out to be connected to the one their father was investigating. This was dropped entirely for later series.
The Star Trek novel series The Rise And Fall of Khan Noonien Singh involves at least one character from almost everyStar Trek episode with characters from the 20th century. Khan (of course), Gary Seven and Roberta Lincoln, Jackson Roykirk, Shaun Christopher and Flint the Immortal from TOS; Guinan, Ralph Offenhouse and Clare Raymond from TNG; Jeffrey Carlson from Deep Space Nine; Rain Robinson and Shannon O'Donell from Voyager.
Gravity's Rainbow has a cast of several hundred characters, and at least for the 40 or so main ones it seems they are all interconnected in multiple ways. (Mapping it all out can be pretty difficult).
Great Expectations. Magwitch, the convict who Pip meets at the beginning, is Estella's father, and Compeyson, the other convict, is the former lover of Miss Havisham (who adopted Estella). The lawyer Jaggers' housekeeper is Estella's real mother and the boy Pip fought with as a child turns out to be Herbert Pocket, who, as a young man, teaches Pip how to be a gentleman.
Dickens is the master of coincidence. The titular character in Oliver Twist is saved from going to prison by the man who turns out to be the friend of Oliver's real father and an admirer of Oliver's mother, who died giving birth to him, though in the musical they simplified it and made him Oliver's grandfather.
A Tale of Two Cities had every major character directly connected to either the Marquis St. Evrémonde or the Doctor he had imprisoned for no real reason.
Lampshaded in The Kite Runner. Amir is not surprised at all to discover that a random beggar on the street knew his mother. Apparently, in Kabul, every single person is related to everyone else somehow or other.
Sarah Dessen is known for this. All of her books seem to take place in one town, or in the beach town next door to it, and it must be a small area because in any one of her books (aside from the first) there will invariably be references to the others.
Examples include: Truth Squad (and Remy's) cameo in Just Listen; Jamie getting Owen from Just Listen to help him with Cora's birthday present in Lock and Key as well as Rogerson from Dreamland appearing (while briefly); Annabel and Owen from Just Listen seeing Macy and Wes from The Truth about Forever at the World of Waffles; and Cora from Lock and Key inviting Remy's mom from This Lullaby to her Christmas party. In Along for the Ride, Heidi is friends with Isabel and Morgan from Keeping the Moon and used to work at Last Chance Cafe.
Murder on the Orient Express. Almost everybody on the train knew each other by working together, but it's not a coincidence; it's been very carefully set up.
In Dracula, the Count's lawyer's fiance's best girlfriend's ex-suitor's former mentor just happens to be Dr. Van Helsing, who knows how to kill vampires. Plus, he moves in practically next door to the ex-suitor's insane asylum. Granted, Whitby wasn't exactly a metropolis back then, but it's still a bit much...
And of course, it's a bit of a coincidence that the first person he targets is Lucy, that lawyer's fiance's friend, which is how Van Helsing actually gets involved.
The girl, Kendra, that Vince falls in love with in Gordon Korman's Son of the Mob just happens to be the daughter of the federal agent investigating Vince's Mob boss of a father.
Christopher Brookmyre novels have lots of subtle nods. Maybe one of the subtlest: the photographer in Not The End of The World is implied to have shot Simon Darcourt's band for their one single.
In the Liaden Universe series, as a result of the Korval clan's Weirdness Magnet and Coincidence Magnet nature, many non-Korval characters find their paths crossing Korval's repeatedly in improbable ways. It sometimes seems as if every minor character in the entire universe is related to Korval in ways that just haven't been revealed yet.
The Big Finish Doctor Who short story collection The Centenarian. It's not just that the titular Centenarian, Edward Grainger, keeps running into the Doctor. It's not even that the Sixth Doctor also met Edward's granddaughter in a previous short story collection. It's that Edward's mother just happens to be a good friend of Lady Louisa Pollard — mother of Eighth Doctor companion Charley Pollard.
The Brief History of the Dead: Pretty much the entire plot of the book. The entire population of The City is made up of people who are remembered by Laura Bird before they and everyone else on Earth except Laura died.
Happens to such a degree in Rule 34 that several characters realize it can't be a coincidence. They are all being manipulated by an nigh-omniscient artificial intelligence.
Xanth To ridiculous degrees, if you haven't gone on a quest with someone, you've gone on a quest with a relative of theirs.
LOST is the epitome of this trope. To give just one example:
Charlie played guitar outside the offices where Desmond had a job interview, who in turn once met Jack while jogging in a stadium, and Jack's father, Christian Shephard, is also Claire's father, met Ana Lucia in an airport bar and hired her, got drunk with Sawyer, and that's all before he died. Word of God says that these are not Easter eggs, but rather a part of the larger mythology.
All the character connections are shown on this page, with this◊ rather impressive graphic.
In Seasons 1-3 such connections only occurred every other few episodes. By the time of Season Six all pretenses are dropped and each episode features cross-character connection at a rate of about once every 15 minutes in the Flash Sideways.
Well, by the end of season 3, they'd stopped doing flashbacks at all. They didn't dip back into the past, so it makes sense that the rest of the show would feature the main characters encountering each other. And the Flash Sideways was some sort of mystical alternate dimension engineered specifically to create this sort of thing.
OnceUponATime uses this trope in the first season when showing events in the Enchanted Forest. But then it wholly embraces it in the second season after we find out that the majority of the main cast are all related in some way. Unsurprising, since it's written by the same team that did "LOST".
Heroes is a user of this trope as well, though to a lesser extent than LOST, with even some characters saying, "We're all connected."
Though the fact that many of the characters are the children of the founders of The Company or were manipulated by it this doesn't seem too implausible.
And the writers of doing a pretty good job of remembering that not everyone has met everyone. For example, it took two full seasons for Matt and Hiro to meet:
(Nathan and Matt arrive at Primatech Paper)
Hiro:(seeing Nathan) Flying man!
Matt: Who is this kid?
The same thing happens with Claire and Hiro, and they have a whole episode centering around it with lampshading of how they never met each other.
Technically, they have met. However, how was Hiro supposed to recognize a toddler he probably didn't even look up to see (he was buried in a handheld video game) when he was little?
Though they sometimes slip up-like how Nathan in early season 2 seemed to have forgotten meeting almost everyone, even people he met before the events of the finale.
On a related note, the fact that new Petrellis keep cropping up certainly implies this.
Charles Deveaux is never actually seen doing anything while he's alive. He's shown unconscious a couple of times, once in Peter's dream, and then he's dead. He seems to be unimportant; just a plot mechanism to connect Simone and Isaac to the Petrellis. But after his death Charles become increasingly important, until by Volume 4 it's revealed that he was the leading founder of the Company.
Ditto Linderman to an extent. Initially he just seems to be a powerful mobster who has very generic interests. While there are a few hints that there is more to his character while he's alive, we don't really begin to find out about him until after he dies.
Community did this in the episode "Heroic Origins" as a parody of this trope's prevalence in works like LOST and Heroes. Turns out and Jeff helped break up Shirley's marriage, Abed got Annie arrested for her pill addiction, Shirley accidentally got Dean Pelton to embrace his Creepy Crossdresser and Camp Gay tendencies, ect.
Specifically, Abed is shown to be the one character who had a hand in bringing everyone together. He compares himself to the villain of their superhero origin story.
Spaced has two flashbacks to childhood showing Tim being chased by a pack of dogs, (giving him a fear of them) and Daisy chasing after them. They don't make the connection. On the DVD Commentary, they mention plans to have all four main characters in the same park as children (with the fifth, Marsha, as a young mother) without meeting, but never did it.
Caprica: Joseph Adama, father of the future military leader of the surviving human race, knew Daniel Graystone, the inventor of the Caprican Cylons.
The Class did this. A group of eight adults who were in the same third grade class spontaneously be re-involved with each other lives, both intimately and in passing.
Six Degrees did the same with a more serious tone.
Misfits got hit with a boatload of this in the time-travel episode. Every character happened to have been at the same club on the same night, and several of them had brief encounters that they had presumably forgotten about the next time they met. This includes their social worker and his girlfriend, who became his fiancee that night, but he didn't have an engagement ring because Kelly and her boyfriend just so happened to break into their car and steal it.
Mad About You discussed this when Jamie got pregnant - they wanted to tell everybody in Thanksgiving, Paul pointed out it would be leaked and spread before the date because people they know usually know each other, using the Bacon numbers as a reference. And in the end of the episode, one person appears to congratulate on the pregnancy... Kevin Bacon himself!
In Friends Chandler's connection to the group started off simply as "Monica's neighbour", but the writers later added that he had also been Ross college roommate, met Monica and Rachel several times and spent regular Thanksgivings with the Geller family. He only became Monica's neighbour because she tipped him off about the avaliable apartment next to her's.
Phoebe, who first met the group through being Monica's roommate, also mugged Ross when they were teenagers. This is lampshaded:
Phoebe: I'm so, so sorry, Ross, I'm sorry, but, y'know, if you think about it, it's kinda neat. I mean, well, it's just that I've always felt kinda like an outsider, y'know, the rest of you have these connections that go way back. And now you and I have a great one!
Charleys Aunt: Jack is Sir Francis' son, Kitty's suitor, and Charley and Babbs' friend. Charley is Amy's suitor, Dona Lucia's nephew, and Jack and Babbs' friend. Babbs is Jack and Charley's friend, and turns out to be the young man who deliberately lost money to Ela's father playing cards when he was penniless and dying, and who loved and was loved by Ela. Sir Francis (Jack's father) turns out to also be Donna Lucia's old suitor. Donna Lucia is Charley's (real) aunt, and Ela's guardian. Kitty is Sir Spettigue's niece; she and Amy are both under his legal guardianship, and are best friends. Sir Spettique wants to marry Donna Lucia. The only character who isn't related to, or in love with note or at least trying to marry, in the case of Sir Spettique, at least one of the others is Brassett, Jack's valet.
Played straight, but almost to the point of parody in The Importance of Being Earnest: Algernon and Jack are friends from the city, Jack wants to marry Gwendolen, who is Algernon's cousin and the daughter of Lady Bracknell. That's all well and fine, but Jack has no biological parents (high society no-no), having been abandoned at a train station as a baby. It turns out that Jack's ward, Cecily, who is Algernon's love interest, is being taught German by Ms Prism, the former employee of Lady Bracknell and also the woman who accidentally abandoned Jack as a baby. It's then revealed that therefore Jack is Lady Bracknell's nephew, Gwendolen's cousin and Algernon's brother. Ironically this is one of the few times where characters turning out to be related actually leads to a happy ending as it gives Jack a respectable background.
Played straight in Wicked where every single character of relevance in the play can be tied to Elphaba. Not unreasonably so since she's the Wicked Witch, but let's sum up. Her teacher is the Wizard's Dragon, her sister is the Wicked Witch of the West, her manservant is a school chum, she saved the Cowardly Lion, the Scarecrow is her transformed boyfriend, the Wizard is her father, and so on and so forth.
Final Fantasy VIII: It turns out that Squall, Zell, Quistis, Irvine, Selphie, and Seifer all resided in the same orphanage...with Edea as its headmistress. And all those flashbacks Squall was having to Laguna were facilitated by another child at the orphanage...who turns out to be his adopted sister...and Laguna turns out to be his father.
And it doesn't even end there: the singer Laguna fell head over heels for in the past, Julia Heartilly, ends up marrying another man when Laguna vanishes during the war. In the present day, Julia's daughter, Rinoa, falls head over heels for Squall.
Fire Emblem. Holy cow there is a ton in every game, mostly revealed through optional conversations. Pretty much every game has had several pairs separated relatives or friends who both happen to join the same army and find each other.
From a series-wide perspective, Fire Emblem Awakening brings back playable characters from every previous game in the series, so that every playable character from the series is separated by no more than four degrees.
In Hotel Dusk: Room 215, the main character (an ex-NYPD detective) stays at a dingy hotel in the middle of nowhere for one night. By morning, he's discovered that every single guest staying there that night is connected to either his former partner Bradley or to another guest in the hotel (and frequently both). This also goes for staff members.
In Ever17, while nobody except Sara and You seem to have known each other beforehand, it turns out that Sara and Hokuto are the children of Tsugumi and Takeshi, You and Coco's fathers designed Sora and Lemu. And You is actually two different people. As you can see from the majorly spoilery bit there, it's... complicated. In fact, this is no coincidence at all, and these people were gathered together specifically as part of a massive Gambit Roulette.
In Remember11, Satoru, the person with whom Kokoro begins to swap minds just happens to be where she was planning on going before her plane crashed. Yomogi (from where Kokoro is) is married to Utsumi (from Satoru's location), Lin (Kokoro's location) used to date Satoru, and Keiko (Satoru's location), is the person who Kokoro was planning on meeting, as well as being the person who killed Yomogi and Utsumi's son. Additionally, Satoru is a student of Kyumeikan University Graduate School, while Kokoro goes to Kyumeikan Women's University. Utsumi gave birth to her twins in a "hospital" (actually a lab of some sort) overseen by (the original) Satoru, leading to those twins being involved in the space-time transfer loops along with Kokoro/Satoru and Keiko/Hotori and providing an important clue to the existence of the third area. Even Yuni, who initially seems to have no prior connection to anyone else, turns out to be the key to the whole Stable Time Loop that ultimately results in the shelter cabin refugees being saved, and as part of his efforts to preserve history might have been somehow involved with Satoru during part of 2011, despite his dislike (according to his TIPS bio) of Leiblich.
In Never7, all four members of the "seminar group", including protagonist Makoto, attend the same university. Yuka, the chosen leader of said group, went to middle school with Saki, who has a summer house on the island. Although the two Morino sisters, Izumi and Kurumi, don't seem connected at first, Haruka (of the seminar group) eventually turns out to be a clone of Kurumi. Even later, Izumi is revealed as the mastermind behind the seminar, whose real purpose was to scientifically test a strange phenomenon by attempting to make Makoto manifest it.
Jade Empire, also of Bioware, had several characters openly expressing their disbelief in the number of connections encountered. As it turned out, Master Li was really Sun Li, brother to the Emperor. Sagacious Zu had saved Li's daughter and ended up unknowingly leaving her with Li who also didn't know about the connection. This also means that Dawn Star is the cousin of Silk Fox, who is also daughter of the Emperor and niece of Li. And both daughters have fathers who are the main Big Bads. And Death's Hand is the emperor's other brother's spirit, bound to Li's old armor. Gah!
In Knights of the Old Republic, Darth Revan, Big Bad Malak's former master, was also HK-47's original owner, the Jedi who inspired Juhani to join the Order, and the one who led the fight against the Mandalorians (including Canderous). The former Dark Lord of the Sith died in a capture mission led by Bastila. Revan got better, however, because s/he's also the player character.
And in the sequel, The Exile commanded the Handmaiden/Brianna's mother and Bao-Dur at Malachor V, a battle Atton also involved in and Canderous fought in on the other side, and ended it by using the Mass Shadow Generator, killing Mira's adoptive family, inadvertently creating Visas' master, and inspiring Revan to commission HK-47 so they wouldn't need such overkill in the future. The Exile was also the Disciple/Mical's intended master before s/he ran off, so s/he's not only a dominant influence in the lives of everyone on that ship, s/he's also responsible for all their significant neuroses. Furthermore, the Exile was a general for Revan during the Mandalorian Wars.
By the time of Mass Effect 3, every major hero of the war against the Reapers has served on the Normandy at some point. Except Admiral Hackett.
The freeware RPG Last Scenario absolutely loves this trope, gradually revealing connections to a certain flashback of seemingly mild importance. At first we simply learn that Thorve grew up with Felgorn and a guy named Wolfram, the latter of whom was killed by a child in a burned-down village. Then we meet Randolph, who was Wolfram's father. Okay, given their current situations, they were bound to meet up again. But then we find out that amnesiac party member Ethan was the boy who stabbed Wolfram, trying to protect his older brother from the soldiers. Oh, and that older brother is now the Big Bad. And the random soldier who chased Thorve and Felgorn off after Wolfram was stabbed is Zawu.
The Reveal near the end of Overlord invoked this. As it turned out the player character was formerly a companion of all the fallen heroes you have spent the game killing, except you had amnesia. The former Overlord, the ultimate Big Bad, has possessed the final hero(one-half degree of separation?) and is also the father of your two potential Mistresses.
Ace Attorney uses this to an extreme in the third and fourth games, particularly the third.
To demonstrate how bad it is: By the end of the third game's last case, protagonist Phoenix Wright is pretty much the only relevant character who is not either related to the Feys or was directly screwed over in a way by the events of DL-6, or both. And even then they indirectly had huge influence on his life by setting up 90 of the 100 reasons he decided to become a Defense Attorney.
In Planescape: Torment, you come across a rather staggering array of people with one degree of separation from one or another of The Nameless One before he got amnesia, including all your party members except Nordom and Fall-From-Grace. Mainly justified in that the game is about a personal quest for identity and therefore you will logically be hunting down people with a prior connection to you, but many of the more incidental side-quests show a rather astounding array of this either way.
Since Brock Samson (see Western Animation) is in Poker Night 2, the game continues the show's tradition of this. It turns out Cave Johnson used to work with Dr. Jonas Venture, and Ash Williams unintentionally ended up becoming one of Brock's ancestors in the 14th century. The second one shocks both Brock and Ash when they find out.
There was another case in which a girl asked Marten out (after he'd gotten with Dora), was declined, and went to Dora's coffee shop, where she found out. Dora goes Clingy Jealous Girl on Marten for not mentioning that he got asked out, and they argue about it, reconcile, and go out to dinner, where the girl is their waitress. A few strips later, Steve has an unrelated chance run-in with the same girl, and winds up trying to track her down before realizing what he was doing could constitute stalking; leaving the building he's in when he realizes that, he runs into her again. They're now dating.
Sluggy Freelance has way too many characters for them all to be connected, but there are many examples of completely random connections, especially between the different alternative realities. This is partly justified in that the dimensions are indeed parallel and often have many similarities, but only partly. Often it's more that the reader can notice the coincidences, not so much the characters, because different people meet different people.
As just one example, the story "Oceans Unmoving" featuring Bun-bun but none of the other main characters features several characters who have been blasted out of time itself, mostly by failed Time Travel devices. A later story shows how one of them got there in the first place and refers to another having got there the same way. Some other main characters see this, but they have no idea Bun-bun has encountered said people, and he himself isn't present at this time to notice the connection (and might not anyway).
At the end of the second volume the strip had a flowchart describing all the major characters and how they all interacted with each other, with Torg at the center. Everyone was one degree of separation from Torg.
In the Ciem Webcomic Series, we have Candi. Her sister Miriam is the notorious Sniperbadger, who is being targeted by Captain Aardwulf. Meanwhile, her boyfriend Donte McArthur has a half-brother whose wife has a sister who is married to Musaran. Milp got inside Candi's head and tormented her for years, but was defeated by Angie, Candi's daughter with Denny. And Milp also had an affair with Duke Arfaas, who has put the hit on Candi. Speaking of Denny, Candi has to rescue him from Gunner Soorfelt, who works for Duke Arfaas and who also is Erin's murderer.
In El Goonish Shive Elliot was one degree of separation away from almost all of the main cast before the story began. Tedd is his best friend, Sarah is probably his oldest childhood friend, Nanase was his girlfriend at the beginning of the story, Justin was saved from bullies by him, and Ellen is his Opposite-Sex Clone. Only Grace and Susan were not initially linked to Elliot; Grace never met any of the main characters before and Susan was initially planned as a supporting character with direct links only to Sarah and Nanase. Several other connections between main cast members before the story started were that: Susan and Nanase became magic users together, Nanase is Tedd's cousin, Sarah and Susan are in the same school club, Justin and Nanase became friends shortly after Elliot saved Justin, Susan taught Sarah how to use Hyperspace Mallets, and Tedd had transformed Sarah before.
Several in The Venture Bros.. Rusty Venture, the Monarch, Baron Underbeiht, Pete White, Brock Samson and Mike Sorayama all went to the same college at the same time. We later discover that Brock and Hunter Garthers sent Billy Quizboy to spy on Professor Fantomas which resulted in the professor being turned into Phantom Limb. While at the college Dr. Girlfriend was one of Phamtom Limb's student. Richard Impossible was also a teacher at the college.
Another example is that the Monarch and Henchman 24 used to be a henchmen for Phantom Limb.
Another example is that Dermott the only kid that Hank ever befriends is his and Dean's half-brother.
Kim Possible's Arch-Enemy Dr. Drakken was a college friend of her father. Tasked with finding dates for their friends, he built crude robot girls instead. The resulting mockery led to his Start of Darkness, storing up trouble for Dr. Possible's future daughter.
Phineas and Ferb... Perry's arch-nemesis is Professor Heinz Doofenshmirtz, formerly married to Charlene Doofenshmirtz, who goes to the same cooking class as Linda Flynn, Phineas and Candace's mother. Doofenshmirtz's daughter, wife, and himself have also met Phineas and Ferb (and Candace, besides Doofenshmirtz note Well, he kind of met her when she switched bodies with Perry, but that's not really relevant.)) but Doofenshmirtz is still not aware that they are the owners of Perry (He actually became aware in the movie but his memory of this was erased - In fact, that was Clark Kenting taken to a new extreme: knowing their pet platypus was named Perry and could fight weren't enough clues for him - Perry still needed the hat to be recognized by Doofenshmirtz). Doofenshmirtz also at one point dated Linda Flynn, and in one episode, he states that he wants to see her again.
And now, as of 'Fireside Girl Jamboree', Doofenshmirtz and Candace have met, as she delivered his cupcakes. Also, Doofenshmirtz's daughter Vanessa seems to be friends with Candace, and Ferb has a crush on her.
Doofenshmirtz once took music lessons from Jeremy (Candace's boyfriend) and in another occasion hired Buford (The Bully who occasionally joins Phineas and Ferb) to bully people for him. In both cases, Perry waited until they left before stopping Doofenshmirtz.
This occurs throughout Robotech as a way of tying together the different groups of characters in the different sub-series. Max Sterling and Miriya Parina, of the Macross cycle, eventually have two daughers: Dana and Maia Sterling, who star in the Robotech Masters cycle and The Shadow Chronicles movie, respectively. Likewise, Claudia Grant of Macross is eventually revealed to have a brother, Vince Grant, who is one of the stars of The Sentinels and who appears in The Shadow Chronicles along with his wife, and whose son, Bowie Grant, stars in the Robotech Masters cycle. Marcus Rush, another of the stars of The Shadow Chronicles, is the younger brother of Marlene Rush, a bit character in the New Generation cycle.
The Roman Empire in the first century (CE or BCE). Rome and I, Claudius get this down to a T. Not only are the entire aristocracy of Rome related six different ways, but they know, grew up with, nearly married, killed the brothers of (etc.) the rest of the important people in the ancient world.
May be Truth in Television, just because over the course of anyone's lifetime, they'll have plenty of these odd run-ins. Not quite as extreme as everyone being related to everyone else somehow. As they say, it's a small world.
By extension, the likelihood of such odd run-ins may be increased depending on the area. A city like London is not only very populous, but it also has a large number of tourists visiting each day. If you're from another area of the UK, there may well be other people from your hometown visiting (or even permanently residing in) London at the same time you choose to visit.
Braddock's expedition (French and Indian/Seven Years War 1755). In a force of a bit less than 2,000 men we have: The leader of the coming revolution AND the next two ranking generals (George Washington, Horatio Gates, and Charles Lee, the latter two in the British army at this time), the military govenor under whom said revolution blows up (Thomas Gage the vanguard commander). AND in the baggage train we have another future general (Daniel Morgan), and a future famous explorer (Daniel Boone) driving wagons. How has this not been made into a movie?
Try playing the handshake game - pick a person, and work out how many people whose hand you have shaken, or had similar interactions with, that it would take to connect you to that person. It's usually not a great deal more than six.
The paper suggesting that everybody is connected by no more than 6 degrees of separation is well known, but this troper is fond of a story connected to it. Professor's giving a presentation on it, and says that everybody is connected to everybody else by 6 degrees of separation. Joker in the back stands up and asks for the chain from the professor to Haile Selassie, Emperor of Ethiopia. Professor stutters that it doesn't quite work like that, when a gentleman in the front row stands up and says that he knows Haile Selassie, and he knows the professor. Two links in the chain. The joker sits down, properly chastened.
Brett Tjeren, a computer science researcher at the University of Virginia, worked out that the average degrees connecting any two Hollywood stars is 2.87. For some it's higher; others, it's lower. The lowest? Rod Steiger, who can be connected to anyone else in Hollywood by an average of 2.11 degrees.
This, of course, led to games like 6 Degrees of Kevin Bacon and 6 Degrees of Hitler (where you pick a random Wikipedia page and follow page links until you get to Hitler's page.)
The professional sports version of this is a Sillinger number, after journeyman ice hockey player Mike Sillinger. No player in the National Hockey League's more than 90 year history is more than six degrees from Sillinger, and at one point in the 2007-08 season, every single player in the 30 team league had either played with Sillinger or had a teammate who had played with Sillinger. It's commonly believed that you can connect Sillinger to Kevin Bacon (here's how it works: Bacon was in "Sleepers" with Ron Eldard, who was in "Mystery, Alaska" with Tie Domi, who was on the Toronto Maple Leafs with Petr Svoboda, who was on the 1997-98 Philadelphia Flyers with Mike Sillinger), but in fact, the Petr Svoboda who played with Domi and the Petr Svoboda who played with Sillinger are differentpeople. However, Domi was on the Toronto Maple Leafs with Eric Lindros in 2005-06, and Lindros played with Sillinger on the 1997-98 and 1998-99 Flyers. Sillinger's Bacon number is 4.
In mathematics, the equivalent to the Bacon number is the Erdos number. Paul Erdős has Erdős number 0. Everyone else has an Erdős number one greater than the minimum Erdős number among the people with whom they've published a paper. So Erdős's coauthors have number 1, their coauthors have number 2, etc.
If you are in a career with a small enough population of occupants, especially one where said people often get shuffled around to different locations (say, if you are a specialist in a small enough career field in the armed forces), you quickly find that everybody seems to know everybody else.
Alternatively, if you have a job where you get to know a wide range of people (like, for example, a church minister, who often also works in multiple places over the years) you often run into people you know, or who know people you know, especially if you often do things that have some connection to your job in your free time.
Michael Caine claims that everyone he knew as a struggling actor in London during Sixties ended up becoming famous like him:
I was friends with Stan Getz, and Lionel Bart, who wrote Oliver! The painter Francis Bacon lived next door. He always tried to get me into his studio to paint me, but he was very gay and I thought, “I’m not going up there.” An actor called David Baron said he was going to write a play, and I said I’d act in it. He called it The Room and he did it under his real name, Harold Pinter. In the sixties, everyone you knew became famous. My flatmate was Terence Stamp. My barber was Vidal Sassoon. David Hockney did the menu in a restaurant I went to. I didn’t know anyone unknown who didn’t become famous.
This happened to Alex and Donna Voutsinas, which they discovered after they got engaged and she was showing him family pictures.