Only You Can Repopulate My Race

He said, I'm from mars and I come in peace,
I have something to ask and it's not discrete
There's a mutated strain in our DNA helix
And you three kids are the ones who can heal it
But were just thirteen man what can we do?
Umm, how should I put this - I think we should screw
What?
On my home planet we can no longer breed
I've been sent as a receptacle to store your seed
Storing our seed!?
Yo, I think he means sex
Man I'm a virgin

We all are - BET

—"Incredibad", The Lonely Island

Oh, boy.

Normally, this would be a fantasy come true for some men out there.

The fantasy of a beautiful girl actually wanting to have unprotected sex with you, with the explicit goal of becoming the mother of your child as a result. Be Careful What You Wish For, 'cause here's the catch: neither of you actually wants it, especially you, the bloke. Due to circumstances running the gamut of prophecies, genetics, curses, or just plain old writer viciousness, you, the bloke, are blessed (or, rather, cursed) to be the only man who can father the child of the female protagonist.

But wait! It gets worse: she is amongst the last, if not the last, of her species/people (or at least the last who can bear children), and the whole race will die if you refuse. And considering that the unfortunate aspiring young mother is more often than not a vampire, goddess, alien or equally super-powered being known for their short-tempers, politely saying "no" alone would drastically shorten your lifespan...

Even if she is reasonable enough to not get offended by refusal, there is always the good old guilt factor, especially if she is a True Companions or equally dear friend, making acceptance and refusal all the more awkward. Hilarity Ensues.

Of course, a lot of these situations could be fixed using artificial insemination, not that that ever happens. (Please note that repopulating the human race is not Truth in Television. Repopulation with one man and one woman would involve too much incest to work; scientists estimate that you need a base population of at least 497 people to maintain proper genetic diversity.)

If this trope is utilized in Fanfic, expect coitus to ensue.

See also Gendercide; in these situations, the race in question is the human race, and it's never pretty for the last man or woman.

Compare Endangered Species, Last of His Kind, Stalker with a Test Tube, What Measure Is a Non Unique.

Sister Trope of Adam and Eve Plot.

No real life examples, please; sorry, we have to impose Wikipedia's "reliable sources" rule on this one.

Examples of Only You Can Repopulate My Race include:

Anime and Manga

Poor Aono Tsukune of Rosario + Vampire is the target of a Succubus and a Snow Girl, both species of which are well known for their poor responses to rejection. To make matters worse, Snow Girls are an endangered species, and he's in love with a third girl.
A rather disturbing adventure in Digimon Adventure 02: A group of borderline Eldritch Abomination Digimon summon 11-year-old (13-year-old in the dub) Hikari to the Dark Ocean with hopes that she can help them to resist the "Dark God who is not a god". Okay, that didn't sound too bad at first... Until they say how she'd be helping. In the dub, they ask her to be their bride; in the original, though, they explicitly say that they want her to bear their descendants so that they can fight the "Dark God".
This is what the Mina's cousins want to do to her (willing or no) in Dance in the Vampire Bund.
Karin has a variation on this. Instead of being the only vampire capable of having children, Karin's blood can grant fertility to other vampires.
In DearS, male lead Takeya becomes this after leaving with Ren and the now fertile DearS on their fixed spaceship, and finding out this is going to be his main job.
This is how Kurama is introduced into Urusei Yatsura. Ataru was chosen, and isn't very reluctant.

Comic Books

Played horrifically straight without a sliver of laughter or irony in Y: The Last Man.
Gold Digger had an inversion of this in one issue. Brittany, Gina Diggers's adopted werecheetah sister, is the Last of Her Kind. Just on her wedding day (to her feline-looking but apparently mostly-human alien boyfriend), what seems to be a male werecheetah suddenly shows up out of nowhere looking for her. Cue awkward. The new 'werecheetah' turns out to be fake but innocent; the ploy was launched by a jealous recurring character who wanted the groom for herself.
Played straight in Valerian: A quasi-human alien species relies on a single hive mother for its reproduction, and she must be impregnated once every generation. The job falls to Valerian. And there isn't even a catch, except for getting temporarily shrunk.
In Alan Moore's Swamp Thing, we learn, in typically cynical Dark Age fashion, that Silver Age superhero Adam Strange was teleported to the planet Rann not to defend them from monsters as he had been told, but because humans are more fertile than Rannians and they needed his DNA.
In Guardians of the Galaxy, Yondu and Photon. That went badly, although the writer at the time had intended it to eventually turn out well.
XXXenophile hints that for one couple this was a sexy role-playing scenario.
Maxima when she is hitting on Superman

Together, we can make a new Almerac, and a new Krypton!

Played for laughs in the Power Girl comics. The Zardoz expy "Vartox" is a ladies' man from outer space - except his sense of style is stuck firmly in the discotheque-ridden 70s. He wants Power Girl to help him repopulate his planet, but explains that she need not physically sleep with him - it is achieved by way of a pregno-ray. It's hilarious because Vartox really is a nice, if clueless and shallow, guy, who means no harm to Karen who is constantly amused by him.
The comic book Brain Camp in which human incubators were only hope of repopulating a race of alien birds.

Films

Vic in A Boy and His Dog is lured from the nuclear-wasteland surface to "downunder" because the sterile men of the subterranean colony need him to inseminate their women. Unlucky for him, the insemination will be of the artificial sort, and he'll be killed after he's impregnated enough of them.
In Hell Comes To Frogtown, titular character Sam Hell is one of the rare fertile males after the nuclear war killed many and rendered most of the rest sterile. The government orders him to go to a city of froglike mutants and mate with a group of fertile females imprisoned there.
- Which is absurd, because the amount of radiation required to induce permanent sterility would kill you if it were applied to the whole body, which is what nuclear fallout would do. Only if applied directly to the gonads could radiation permanently sterilize a person without killing them. Temporary sterility, lasting up to a few years, however, is a possibility for radiation doses that are potentially survivable.
  - I'm sure they accounted for that.
Played with in Waterworld, as not a means of repopulation but inbreeding prevention: inhabitants of atolls (floating settlements) provide nubile females to visitors (such as nomadic sailors coming to trade). This brings problems to the protagonist when he's not willing to take the offer.
There's something of a subplot in Immortal like this, at least as far as "rare person who can mate with gods."
In the 2011 All CGI Cartoon Rio, Blu is the last blue macaw left, and the movie focuses on making Blu worthy of mating.

Literature

Spoofed in Terry Pratchett's Interesting Times. Rincewind is stuck on a tropical island and is found by a tribe of lovely Amazons (a regional curiosity for their white skins and blonde hair) who have lost all their men to a highly specific plague and require him to repopulate their tribe. Sadly, Rincewind is magically "rescued" before he can obtain his greatest fantasy (potatoes).
A female variant appears in Mercedes Lackey's "Oathbound" stories. An oath-sister of the last survivor of a Shin'a'in Clan agrees to physically reestablish the bloodline (with great success). Though she doesn't provide all the clanmembers - many were immigrants from other clans. They just needed a core of people from the original clan, and evidently unrelated oathsisters count. Since the oath itself is agreed to by the Shin'a'in goddess, it's probably a case of a goddess did it. Plus the fact that not only do other clans exist for the blood to be introduced, but the clans are bound as much by tradition as blood, not to mention that most are inter-married anyway.
Older Than Steam: Appears during a hilarious incident in Journey to the West. Slight subversion: while the women are still able to reproduce, Xuanzang was still the first man ever to come to their kingdom. Pity he's a monk.
Variant: In Garth Nix's Old Kingdom trilogy, it is revealed as the end of Lirael that Lirael's mother Saw her child in a prophetic vision, and knew two things: 1. The child had to be fathered by the Abhorsen, and 2. The entire world would end if this child did not exist. Fortunately, the Abhorsen seemed to be a rather... understanding gentleman about it all...
The Unfortunate Implications of this trope usually never enter the picture. The Metamorphosis of Prime Intellect is an exception. Having just wiped out the rest of humanity by Logic Bombing the titular sufficiently advanced AI, there is only the female lead and one male left on Earth. After having a son and daughter, she implements her repopulation plan, which starts out with the father impregnating the daughter and her son impregnating her and somehow goes from there...
Also dealing with the Unfortunate Implications, in Octavia Butler's Lilith's Brood series, humanity has been basically sterilised by aliens who intend to interbreed with them. A small pocket of runaway humans is surprised when a young girl becomes pregnant after a sexual assault by a passing stranger. Deciding that this is the only way to perpetuate the pure-human species, the rest of the group separates the mother and child, raising the baby until puberty, when they then force him to impregnate his mother. By the time anyone finds this little colony, the resulting generations are suffering nasty mutations.
After killing off most of the members of his father's race, including all the men, Cal Leandros finds out that the only surviving Auphe are females, and guess what they want him for now...
The French comic Castaka (by Jodorowsky) is really heavy about this trope. To make a long story short, one clan has doomed the other clan by making all males sterile, which will lead to an inevitable decay. However, the chief's wife is pregnant (from a rape...), and it's a boy! So, the young prince has to repopulate the entire clan by himself. Which turns into a full-time job. Beginning when he was twelve. Squick.
Kurt Vonnegut's Galapagos isn't a completely straight example, but it is notable for averting both the lack of artificial insemination (done by hand, literally), and actually showing the effects of the implied incest and genetic bottleneck.
Saphira in The Inheritance Cycle is painfully aware that she's one of the last dragons in the world, and the only male she's aware of is the partner of the Big Bad. When she finds out there's another surviving male dragon, she approaches him, but he refuses. She doesn't take it well.
The Alfred Bester short story "5,271,009" explores this scenario (and a few other cliched-even-in-1954 sf wish-fulfillment scenarios) for the sole purpose of poking holes in it.
In the scifi novella The Night Faces, the folklore of a Lost Colony attests that the planet's population descend from just one man and two women, one light-haired and one dark-haired, who survived a starship crash. Justified, in that the story turns out to be a metaphor for the colonists' Jekyll and Hyde nature, as they periodically change from peaceful to violent in response to a psychoactive spore in the atmosphere.
In Mikhail Ahmanov's Ash, a bomber pilot named Hadas Kewm crash-lands on Garuda, the colony Earth is bombing to hell for at least a decade. He is captured by a group of Garudan colonists, who live in a subterranean city. Most of their population has degraded due to radiation, underground living, and cannibalism. Hadas is told he'll be impregnating females in order to inject fresh, uncontaminated DNA into their gene pool. At first, Hadas thinks it may be fun, but he finds out that the brutally-efficient Garudans aren't about to leave such an important thing to chance. They artificially "stimulate" him with electricity and collect the semen for artificial insemination. Occasionally, to help him get excited, they bring in a naked woman without letting him touch her. Needless to say, he doesn't enjoy the experience much.
In David and Leigh Eddings's Belgariad and Mallorean, the Marag people were wiped out long ago by their neighbors because of gold. Centuries later, the protagonists find a Marag woman as a slave in another neighboring country, referred to in prophecy as "The Mother of the Race That Died"; she becomes attracted (for several reasons) to a zealot sworn to celibacy, who returns the affection (despite himself) but holds to his vow... right up until his god tells him that isn't what the god had in mind. By the end of the series, it's mentioned they have a small army of children and counting. (Mara is implied to be giving it a push.)
Poul Anderson's After Apocalypse handles the need for a gene pool. A handful of women survive, and when they find a ship of men, discussion almost immediately begins about the way they will need to practice polyandry to maximize the number of genes they save for the next generation.
In Roger Zelazny's story "A Rose for Ecclesiastes", the protagonist falls in love with a woman of the dying Martian race; he doesn't learn until afterwards that the whole thing was this trope and that the woman was not happy about having to sleep with him (each of them fulfilled a described role in a Martian prophecy about the only way to save their race, even her not being in love with him was part of it).

Live-Action TV

Some elements are averted in the Doctor Who episode "Delta and the Bannermen". Delta and her daughter are the last of her species, but don't take any action to do anything about that. Billy secretly takes Chimeron royal jelly to transform himself into a Chimeron-Human hybrid without Delta's knowledge so that he can mate with Delta. The variation here is that he is perfectly willing to go through with all this, whereas Delta is reluctant—aside from Billy's sacrifice, the transformation is not entirely safe, and, as the Doctor points out, even in his new form, inter-species breeding could result in "the most terrible mutations".
Star Trek: The Original Series had "Wink Of An Eye," where a species of Human Aliens has become hyperaccelerated until Time Stands Still for them, but it left their males infertile, and so they need to steal Kirk et al for breeding purposes.
- And another episode had the inversion of this—A massively overpopulated planet that doesn't believe in suicide or contraception and is immune to sterilization tries to get Kirk to sleep with a local girl to spread a disease to her people and increase the deathrate, I kid you not. They even inexplicably build a huge copy of the Enterprise interior to make him feel "at home". Really, there are much less embarrassing ways to get help. Like actually asking for help. But Kirk's gotta get his recommended weekly allowance of poontang...
  - A slight variation in the original pilot "The Cage," where the Talosians were breeding a race of humans as slaves to rebuild their planet for them. When Captain Pike resisted mating with the only female available, they brought down two of his crewman, so he could chose from a blonde, a brunette, and a redhead (although logically they wouldn't have wanted him to pick just one, this was network television in 1965).
A Star Trek: Voyager episode has perennial Chew Toy Harry Kim kidnapped by Lesbian Space Vampires for breeding purposes.
On 3rd Rock from the Sun, when Sally saw snow for the first time, followed by a blackout, she became convinced the world was ending. She was alone with Dick's student Leon at the time, who explained that he would have to impregnate her in order for the human race to survive. Much to Leon's disappointment, the lights came back on just when they were about to go at it.
The Farscape three-part episode "Look At The Princess" hits most points of this trope, replacing "repopulate my species" with "continue the royal lineage". The Sebacean princess was the victim of "DNA poisoning" by her scheming brother, which made her incompatible with Sebaceans, but fully compatible with John. Drama and politics ensue.
Played completely straight in one episode of Andromeda. This is complicated by the fact that the alien queen who successfully mates with Hunt also needs her planet to pass through a gas cloud which the crew, presuming it to be a bad thing, temporarily moved out of the planet's path.
- Oddly, the Nietchean who is also present (from a society where being a father is considered the highest honor achievable) doesn't bring it up when she announces that choosing Hunt was essentially random.
In the Red Dwarf episode, Psirens, the titular GELFs attempt to lure Cat down to an asteroid by claiming that they are part of a dying race where only women are left, and that they could only be saved if he made love to all of them.

Music

From The Lonely Island's album Incredibad, this is the subject of the song with the same name. Any hesitation involved is rather brief, however.

Video Games

This was going to be Penn's eventual job for the Nereids once he grew up in Soul Nomad and The World Eaters. It became a moot point once the Nereids became the hosts of refugees from the nearby kingdom of Raine when Feinne destroyed it -- apparently, quite a lot of the surviving males got on well with the nereids, as Juno's ending reveals.
A very nice example from the The Witcher saga. Dryads are an elven subrace, and they need men, but they hate humans as a species. Geralt actually offers the kidnapped man some tips: "Don't think of yourself as a sex god, talk about trees and weather, when you are not needed, go away."
Raidou Kuzunoha VS King Abaddon has a female example, where the Tento Lords who live near Tsukigata Village need human women to reproduce, and they offer the use of Luck Locusts to the villagers in exchange for women of the Tsukigata family.
In one of the endings to Star Fox Command Fox apparently ends up filling this role for Krystal's race, if their son's fur coloration is any indication.

Web Comics

In Fans!, one character, a pudgy, hairy ubernerd-type, had a sort of what-if mini-arc where he was the last human being alive, and aliens asked him to re-sire humanity, using reproductions of his friends made using his memories. It skips to decades later, as the "Allfather" is managing the burgeoning human population, and taking steps to reduce the inevitable effects of inbreeding due to the limited gene pool.

Web Original

Cracked.com's 6 Disturbing Unanswered Questions from Children's Movies shows what would probably happen after Rio: the implied Brother-Sister Incest in the next generation would result in infertility.

Western Animation

Leela of Futurama met a fellow Cyclops and realize that she has to marry him in order to repopulate the planet. It turns out to be a scam of a shapeshifting alien and it turned out that he was pulling the same trick with four other oddly shaped alien babes.