Shapeshifting Lover

How'd he wind up with a fox like her? It's ... complicated.

A folklore trope which appears throughout the world a lot. The story typically goes something like this:

"A man spies a group of magical shapeshifters bathing. Seeing that they must shed their creature skin when they transform from a creature into a beautiful woman, he steals one of the skins. Unable to transform and join her sisters, one poor creature is left behind. The man makes the abandoned one his wife. One day, many years later (sometimes after bearing children), she finds the skin and may finally return to her kin."

It's a motif, sometimes known as "The Animal Bride" tale, that crops up all over the world. Though the details of the story are different, the core story is more or less the same.

A popular variation has a creature fall in love with a human and willingly take on human form to marry him. But when he finds out about it, often by breaking a promise, she must leave him.

Occasionally, this is used as an introduction to the Fairy Tale type, The Quest For the Lost Wife. It is common enough to be its own subtype, The Swan Maiden.

A Gender Flip version of this Fairy Tale has the heroine wooed by an animal; once she consents to marry him, he turns into a man at night. But when she violates a prohibition—frequently burning his animal skin or actually seeing him in human form—he must leave her. This results in the Fairy Tale type known as the Search for the Lost Husband. Unlike the female version, the male's Involuntary Shapeshifting is usually the result of a Curse.

The Wonder Child may be animal in form, but the wedding usually inaugurates a period where he can switch back and forth, or completely breaks the form.

Examples of Shapeshifting Lover include:

Anime and Manga

Considering that Princess Tutu is influenced quite a bit by the ballet version of Swan Lake, it's probably no surprise that the anime indirectly references this legend, as well. Tutu sometimes appears as a swan to people, and was in love with the Prince from her fairytale—but she's the one who has to hide something, instead of the Prince.
Tears to Tiara uses a variation on the selkies, Llyr is a 'sea elf' who uses a seal pelt to transform into a seal. When Awarn accidentally burns it, she announces she is his wife (sea elves give their husbands their pelt, or must marry anyone who steals it).
The most famous modern take on this is probably Ayashi no Ceres, wherein the spirit of a Tennyo awakens in some of her female descendants to wreak havoc on the rest of her family when the descendant reaches 16.
Setsuna of Mahou Sensei Negima is, in fact, a Half-Human Hybrid of the Tengu variety; after revealing her tengu traits she tries to skip out (per 'law of her people' and probably personal insecurities) on the crew. Negi convinces her to stick around.
Every member of Tsukune's Unwanted Harem in Rosario + Vampire is merely disguised in human form, the exception being Yukari, whose species looks human by default. Their true forms are all cute monster girls.
Crane Wife is parodied in Hare + Guu, where Guu offers Hare shaved ice in the middle of a snowstorm, he gets pissed off. She goes into the back room, telling Hare that he mustn't look at what she's going to make. He sees a silhouette of a crane through the window on the door, bursts in and sees... Guu making more shaved ice.
An episode of Pokémon has the ghost of a beautiful woman seducing James and Brock. This gets awkward when the ghost turns out to be a male Gastly.
- Not as awkward as you'd think — it turns out in the end that the Gastly's in it to propagate the REAL ghost's legend, and to make a little money on the side (it even materializes a cash register as it's talking to said real ghost). How does he make money, you ask? He disguises himself as a crazy old lady and sells fake wards and charms).
- In the episode, "Just Waiting on a Friend", a Ninetales takes the form of a woman to lure Brock to her mansion because of mistaken identify. She had thought that Brock was her long-lost master. Given that the Ninetales are Kitsunes, it's surprising how long it took them to reference this trope.

Comic Books

An issue of Ninja High School features this almost exactly; Jeremy, visiting his grandfather in Japan, aids an injured crane, and a girl shows up to reside with them. Of course, she pays them back by working as a software programmer. In crane form.
The Good Neighbors has two swan maidens - well, one maiden and her brother - among the many, many fae in the college town at the center of the book. The whole folk tale is rather deconstructed, as when their skins are taken by a mortal, the girl is effectively forced into sexual slavery, and it's up to her brother to kill her and end her torment, as he can't act against her captor either.

Film

In one segment of Tales from the Darkside, a failed artist, Preston, witnesses a gargoyle, who makes him swear never to reveal what he has seen. Shortly thereafter, he meets Carola; they fall in love and marry and have two kids. He eventually tells her about the gargoyle. She is the gargoyle; she and the kids transform, kill the man, and fly into the night.
Green Snake, based on a Chinese folk tale, involves a serpent-spirit who seduces a young man by posing as a beautiful maiden.

Folklore and Mythology

The Pink Dolphin of the Amazon is thought to take human form at night, whereupon it seduces young, impressionable girls with its charm and impregnates them, returning to the river by the morning. Typically, when a girl in that region turns up pregnant and the father is unknown, fatherhood is attributed to the dolphin. A striking feature is that its blowhole remains even when the dolphin is in human form, which demands that it use a hat to conceal it when on land. Another identifying feature is that the dolphin people wear white while on land, and the dolphin-fathered children tend have dolphin-colored skin.
There is an Inuit legend about a petrel who is in love with a beautiful maiden, and transforms himself into a man so that he may marry her; however, his eyes are still those of a petrel and so he wears snow goggles to hide them. When the maiden takes them off, she sees his eyes and the spell is broken.
Swan Maidens - Common to mainland Europe, and Russia. The women (occasionally men too) in question are normally swans, but they leave their feathered cloaks behind when they bathe as humans. This has influenced many stories, modern and old including the ballet Swan Lake, Swanmays in Three Hearts and Three Lions and Dungeons & Dragons, Anita Blake's Swan Men, etc.
- Fairy Tales incorporating this in the Quest for the Lost Wife include The Swan Maiden and The Three Swans.
- Fairy tales that end with the wife's escape include The Swan Maiden.
Selkies - Celtic and Nordic legendary seal people. If a man captures a female Selkie's skin, she is in his power and must be his wife, but she will return to the sea as soon as she finds her seal skin. In some versions of the story, the children follow their mother and transform into seals, or alternatively, drown. In others, most famously the film The Secret of the Roan Inish, the children cannot change as they are (mostly) normal humans and are left behind (and confused unless their father explains what happened). The male Selkies are seducers of women. There is a similar American Indian story of a seal boy. This again crops up often in modern fiction and other works, and has also inspired a Dungeons and Dragons race.
Melusine - There are many versions of this romantic French tale. In one version, Melusine fell in love with a human and appeared to him as a beautiful woman. When they were married, she made her husband promise that she would have some time to herself each week. Wouldn't you know it, one day he breaks his promise and sees that she is actually a dragon (depending on other variants, she's even half-snake). Melusine is forced to go back to her family, but her children stay with the humans and a group of French nobility claimed to be her descendants for many years.
The hero of East of the Sun and West of the Moon is a bear and once he wins the heroine, he can only take on his human form at night. Similarly with The Black Bull of Norroway, The Brown Bear of Norway, The Enchanted Pig, the dog in The Daughter of the Skies, and The White Wolf. When the heroine violates a prohibition, he must leave her. However, when she finds him after a long search, she is able to recover him.
- Hans My Hedgehog is yet another variant. It is probably best known for being dramatized in an episode of the cult favorite Jim Henson series, The Storyteller.
In The Myrtle, a woman wishes for a child, even a sprig of myrtle, and gives birth to one. A prince is so enthralled by it that he buys it from her, and the myrtle changes to a Fairy in his rooms at night.
In The She-Wolf, the bride was a wolf, with a wolfskin, before the miller's son nailed it down so it would not fly back to her; then, later, her son tells her where to find it.
In the variants of the Chivalric Romance The Swan Children, the bride is more or less clearly a swan-maiden; she gives birth to children who are first exposed and then transformed into swans by removing the chains they wear about their necks. When this is discovered, the children are changed back by restoring—except that one chain was melted down, trapping that child in swan form.
Tennyo (Heavenly Maidens) - Japanese imports of Indian and Chinese Buddhist figures. The males are called Tennin. They don't change from animals but they do need a feathered garment (a hagoromo) to fly back to the heavens. The Noh play Hagoromo features the core story where the the garment in question is stolen.
Kitsune (fox-spirits) and Tanuki (raccoon dog spirits) - Japanese trickster animal spirits. They don't leave skins behind, but they sometimes transform into beautiful women and marry men. They must leave if the man discovers their identity. Sometimes they are malicious and sometimes they are kindly. They are also sometimes female as humans, but male in their true animal forms.
- Not just male; among the best-known traits of the Tanuki are its ridiculously large testicles.
  - That's nothin'. On occasion it's implied that both sexes have the testicles, which, as far as fantastical creatures go, makes a certain amount of sense (dwarf beards, anyone?), but considering the tanuki is also a real animal is just plain weird.
- The strong vulpine predisposition to womanhood is also by no means binding; they are known often to have impersonated men, although a lower percentage of these are for romantic purposes.
  - On that note, there is a myth of an idiot who gets a cute young fox drunk and lets it snuggle up next to him for the night. When he wakes up, he finds a naked boy next to him right when his parents look in.
  - The recognized psychological condition of being kitsunetsuki, thinking you're possessed by a fox, is pretty much the Japanese version of clinical lycanthropy, but spent a very long time as a general diagnosis for crazy people. A lord once sent a very sharply worded letter to the god Inari for the inconvenience a possessing fox caused his household. True story.
  - One particularly famous positively-depicted Fox Wife is Kuzunoha, mother of the Japanese Merlin. (A guy with the bonus cred of actually having existed.)
Gumiho are the Korean version of the nine-tailed fox. They occasionally seduce men, though normally they're trying to win his heart (or liver) in a more literal sense.
Toyotama - Her story is remarkably similar to that of Melusine's. Once again, she was a dragoness who turned into a beautiful woman and married a human. Once again, it didn't end well...
The Crane Wife. A poor man finds an injured crane, and nurses it back to health. It flies away, and soon a beautiful woman shows up and marries him. She helps make him wealthy with her weaving, with the condition that he never watch her weave. He gets greedy and breaks this rule, and sees her in Crane form weaving her feathers into the silk. She then leaves once her identity is discovered.
A Japanese story featuring a yuki-onna followed Melusine's path in a way. A man got lost in a blizzard and this snow woman showed him the way out: she made him promise never to speak of the encounter to anyone or she would kill him. Later this man meets a beautiful woman and marries her. Many years, and a son, follow and one night, after a bit of sake, the man tells his wife of the yuki-onna. The wife stands up and reveals herself to be the yuki-onna, immensely annoyed, and leaves but does not kill him. It varies on whether her reason for sparing his life was that she had given him a son and hence had some sort of emotional attachment or that since he hadn't technically told anyone else.
Second husband of Inuit sea godness, Sedna turned out to be a petrel-spirit in disguise. In some myths it’s the reason she left him later. Other Inuit legends claim that in the The Time of Myths it was normal for spirits to cross border between human and animal world and vice versa. Many of them are love stories.

Literature

The Arabian Nights features the story of Janshah's pursuit of Shamsah. She was a Djinn who also turned into a swan by using a feathered cloak. She managed to ferret out that her swan-cloak was buried under her (new) palace the minute her fiance buried it.
- A somewhat modified version of this story appears in Lotte Reineger's The Adventures of Prince Achmed. Peri Banu, a Fairy woman who uses a feathered gown to fly around as a bird, isn't too upset when the prince proposes to her, though.
The book The Sterkarm Handshake features no actual swan-mays, but the Shapeshifting Lover legend does feature heavily in the story. The main female character, Andrea, is part of a group of time travellers from Twenty Minutes Into the Future who travel to medieval times. When in the past, the time travellers say that they are elves. Andrea falls in love with a man from the past, but he is wary of entering into a relationship with her because swan-mays, as he thinks Andrea is, always leave their human lovers eventually. (Guess what happens at the end.)
Megan Whalen Turner referenced the Selkie legend in one of the short stories in her book "Instead Of Three Wishes". In the story, a Selkie who has been searching for her coat for many years enlists a young girl to help her find it, after the man who tried to force her to marry him hid her coat in a painting.
In the dark fantasy novel, The Folk Keeper, the heroine has an unusual affinity for the mysterious creatures of the title. Turns out she's a half-Selkie. She tries to escape in her seal-form by wearing her magical skin, but it had been too damaged by the villain, making it impossible to ever remove it. Not wanting to give up her human form permanently, she rips off the skin before it's too late and loses it in a storm. She may be separated from her family, but can still have a connection to the sea without the skin, and at least this way she can stay with the nice human guy who loves her.
Selkie Girl by Laurie Brooks is a retelling of this story. The main character Elin Jean has had webbed fingers her whole life. She finds out that her mom is a selkie. Elin then becomes a selkie as well.
In the Belgariad and prequels, Poledra is a variation, since she genuinely decided to be Belgarath's wife. She is capable of switching between forms at will and is evidently as immortal as Belgarath.
"Gargoyles", one of the stories in Tales from the Dark Side: The Movie, referenced this folklore trope. A gargoyle came to life and rescued a man from muggers, exacting a promise never to tell anyone what had happened. Later, the gargoyle appeared to him as a beautiful woman, whom he married and had two children with. When he broke the promise to her (he didn't know who she was), she and both the children transformed back into gargoyles in a very horrific process and killed him.
- Although there is no shapeshifting involved, this is probably taken from the tale of the yuki-onna, where she first makes the man promise that he will never tell anyone of their meeting, and later marries him without his recognising her. The gruesome ending doesn't occur, though.
The novel The Woman Who Loved Reindeer is a rare gender-flipped version of the story. It is pretty much Exactly What It Says on the Tin. The woman of the title falls for a legendary being known as a "Trangle", essentially a reindeer that occasionally looks like a man and transforms by removing his deer skin. There is an interesting complication in the relationship in that the Trangle is extremely aloof and uncomfortable around humans, and it is implied near the end that he will show his lover how to transform into a reindeer herself so that their relationship can actually get anywhere.
Elizabeth Marshall Thomas' palaeolithic romance The Animal Wife is a realistic and anthropologically rationalised story about an incident the like of which might have given rise to the widespread "animal wife" folk-tale motif. Not that anyone in the story thinks the "wife" is a shape-changer, but you can see where the story would go once it was retold a few times.
- The "wife" (a.k.a. victim of kidnap, rape, and enslavement) is really just a woman from another culture. And as her culture is neolithic the writing is on the wall for the jerkass protagonist and his people.
Peter S. Beagle has a short story called "The Tale Of Junko And Sayuri", where a hunter wounds an otter and takes it home with him to nurse it back to health. Once the otter is healed, it transforms into a woman and becomes his wife, who uses her power to help him move up in life, all the time not knowing what exactly she is. It turns out she's an ushi-oni.

Live Action TV

Miho from My Girlfriend Is a Nine-Tailed Fox is a gumiho (see folklore section) who believes that she can become human if she spends 100 days with Daewoong.

Music

Heather Dale has a song about a woman/selkie pair where the woman finds an old selkie coat and turns into one herself.
The Crane Wife is referenced in The Decemberists' album of the same name, which has a song explaining the story.
- They seem to like this trope. In their album The Hazards of Love, the main singer is able to change into a fawn, and takes advantage of this power to, er, "initiate" his relationship with the innocent Margaret. Being a human adopted by the Queen of the Forest has its perks.

Tabletop Games

The Swanmays of Dungeons & Dragons are a secretive all-female order of humanoid rangers and druids who can turn into swans.
Selkies are aquatic fey in Dungeons & Dragons and often travel among surface races for a time, sometimes dallying with the surfacers, but almost all eventually return to the sea.
Selkies are also one of the kiths in Changeling: The Dreaming. Their sealskin coat can take the form of any garment from a peacoat to a belt, and they wither and die (well, they forget all about fae existence until the next incarnation) if they spend too long away from the coast.

Video Games

The basis of Iroha's Backstory in Samurai Shodown Tenka. During one of her super moves, during which she disrobes and attacks the opponent behind a screen, her silhouette briefly flickers into that of a crane's.
History books in Pokémon Diamond and Pearl reveal that the people in the world of Pokémon have these myths about Pokémon. Squicky - but hey, if Skitty and Wailord can get it on, why not people, too?
Subverted in Da Capo with Yoriko. She's a girl with cat ears, and is indeed a cat that transformed into a girl. However, she transformed into the form of her owner, and her owner was piloting the body. At the end when the tree dies, the girl's real body wakes up and transfers into his school, at which point they enter a real relationship.

Web Comics

The selkie legend appears in Hanna Is Not a Boy's Name, with a little bit of deconstruction: Mrs. Hatch is a selkie, and since Mr. Hatch stole her skin, she's been stuck as his human wife for nearly two decades. She hates her husband and her son, and looking for the skin got another character killed.
In Wooden Rose, Aidan Thorne is continually having to hide from Nessa that he's started to turn into a tree while he's wooing her.

Western Animation

The Pink Dolphin legend shows up in The Wild Thornberrys, but with a girl who Eliza believes to be a shape shifting River Dolphin who wants to transform Debbie into a River Dolphin because she wants a friend and is lonely. Debbie doesn't transform but it is never confirmed whether the girl in question was a Dolphin or not. Knowing about the above story gives the episode a distinctive lesbian subtext.