The "Soulmate AU" is a kind of fanfic or fanart that revolves around a setting where everyone has a One True Love, however there is a form of Red String of Fate that ties the soulmates together. Usually these soulmates are romantic, though works with platonic soulmates exist for those who enjoy Heterosexual Life Partners, Romantic Two Girl Friendships, and Platonic Life-Partners.
There are numerous ways for this concept to work. The most common is the "soulmate mark", which is a mark that soulmates share. When the mark appears and what it says varies Depending on the Writer, though the most common interpretation is that people are born with either the first words their soulmate will say to them or their soulmate's name on their body. Another common way for soulmate AUs to work is for people to see in greyscale until they meet their soulmate.
This type of fanwork is most popular on Archive of Our Own and Tumblr. The earliest known cases of the "Your soulmate's name is written on you" prompt date back to the Glee and Sherlock fandoms circa 2011. The 2009 film Timer might have helped spark this form of fanwork. In it, for a fee a person can get a device that counts down to the point where you meet your soulmate. However, it only works if both soulmates wear a device.
Sub-trope to Alternate Universe Fic.
- Colourblind Soulmate is a Haikyuu!! Fan Vid based on the AU. It uses the "people can't see colours until they see their soulmate" version of the idea. Tooru and Hajime meet when the latter transfers to their school. They become a couple but Tooru starts seeing in monochrome again one day. It turns out Hajime is dying of cancer, and now Tooru won't be able to see in colour for the rest of his life.
- Yuri!!! on Ice:
- all we know is a Yuuri/Viktor Fan Vid is of the "you see in monochrome until you meet your soulmate" variety.
- Unspoken is a Yuuri/Viktor soulmate AU fic. In it, when a soulmate compliments you the words appear on your skin. The problem is, Yuuri is mute in this fanfic.
- Unwritten is a Yuuri/Viktor fic. In it, whatever a person writes on their skin becomes written on their soulmates skin too. Since Viktor is Russian and Yuuri is Japanese, a Language Barrier is involved.
- Soulmark is a fic where this is invoked. Anna goes to the trolls and asks for a soulmark in order to prove that Kristoff is her soulmate. It turns out her sister Elsa is instead.
- Love Worth Fighting For is a Crossover Ship fanfic involving Mulan. In it, everyone is born with a soulmark of their soulmates name on their hand. For her entire life, Elsa thought her mark was gibberish, however it turns out to be Chinese calligraphy. Her soulmate is Mulan.
- rise like the break of dawn is Brave crossover one-shot that ships Elsa with Merida. It uses the "your soulmark is of the first words your soulmate says to you" variant.
- hello goodbye ('twas nice to know you) is a Harry Potter fanfic where Draco and Harry are soulmates. Draco notices one day that his soulmark, which changes depending on the soulmate's thoughts, seems like they belong to Harry.
- J'ai fort lu Platon, mais rien ne m'en reste is a Les Misérables soulmark AU, using the "soulmate's first words" variation, that mostly consists of Enjolras and his amis discussing the implications of the concept (like the fact that a soulmark is completely useless to the many people in 19th-century France who were never taught to read). It deconstructs the common "ugh, I hate this person I've just met but apparently they're my soulmate" plot by specifying that if two people haven't grown into each other's soulmates yet when they first meet, their soulmarks won't record their actual first words to each other but instead the first thing they say, however much later, when they have grown into soulmates. This also sets up the fic's big dramatic irony: that Enjolras has given up on finding his soulmate because his mark is the unhelpfully non-unique "Vive la Republique!", while Grantaire has given up on finding his soulmate because his mark says nothing at all.note
- An Ever-Fixed Mark is a Pride and Prejudice soulmark AU, using the "soulmate's name" variation. It's a deconstruction, critiquing the idea of One True Love that comes bundled with the soulmark concept. In the fic, each person gets only one part of their soulmate's name, making the whole business much less certain. Elizabeth Bennet's mark says "Fitzwilliam", which tips her over into starting a romance with Colonel Fitzwilliam instead of remaining single long enough to get on first-name terms with Mr. Darcy.
- Not Alone Anymore is ship fic between Cat and Kara. Cat spent almost forty years of her life without a soulmark until one day it appeared. When Kara arrived on Earth, she received her soulmark.
- Signs is a Kara/Lena and Alex/Maggie soulmate fic. It uses an interpretation where everyone has a compass pointing towards their soulmate. Kara, being an alien, doesn't have one.
- Your Mark on my Skin is a Stiles/Derek Teen Wolf fanfic. People have marks on their body that represent their soulmate. Stiles has known Derek is his soulmate since sixth grade but Derek took a lot longer to figure it out.
- In the fic With Your Crooked Heart, most people (except those supposedly incapable of love) have words on their forearm which appear as if by magic at some point in their lives, usually during childhood. The words are in the handwriting of your True Love and may be a name, address, or cryptic clue like a poem or obscure reference. When the clue is obvious, like an address, you can hurry fate along by turning up on their doorstep, but if its as vague as a line of poetry, you may have to get to know your True Love before the clue begins to make sense.
- In the TiMER-inspired fic Blue Veins, everyone has a magical configuration of veins near the surface on the inside of the wrist that count down to the moment you meet your True Love.
- In the fic Put a Smile in Your Name, everyone is born with the first name of their True Love in their True Love’s handwriting on their palm. Databases of this information exist and, for a fee, matchmaking companies will check for any matches between your name and the name on your palm.
- In the fic Finding John, everyone is born with the first name of their True Love like a tattoo on the inside of one finger. With only a limited number of first names, it’s usually not enough information (unless you’re The British Government) to lead you to a person but once you meet your True Love, they’ll have your name too and the particular color and shade of your names will match.
- This trope is defied in the fic, To the Limits of Your Choice when Sherlock chooses not to care, or perhaps not to accept the consequences of acknowledging the person symbolized by the soulmate mark on his wrist. When John finds his soulmate, Sherlock asks John to choose between camaraderie with him and romance with her and John also defies this trope, choosing to continue adventuring with Sherlock.
- Cherish Me is a short A Way Out AU fanfic, centered around the headcanon that the game's two protagonists, Leo and Vincent, are soulmates who have Touch Telepathy, which gives a plausible explanation as to why they were able to work so well together. It also explains why, in the final battle, Leo and Vincent experience each other's memories every time they attack each other. The difference is that both Leo and Vincent realize they are soulmates, and end up surviving in the end.
- A Deconstructive Parody in the Avatar: The Last Airbender fic "Now Kiss," for the rarepair Sokka/Mai.
- The Legend of Korra:
- The fic Rumble mixes the soulmate AU with the equalist!Asami AU. Asami is an Equalist spy on a mission to befriend the Avatar. However it turns out Korra is her soulmate. The fic uses a variation of the AU where soulmates feel each others pain.
- They say that true love hurts. Well, this could almost kill me is a Korrasami fanfic where soulmates feel each other's emotional and physical pain.
- RayDrawlings on Tumblr has a series of "soulmate mark AU" fanarts based on Miraculous Ladybug. Marinette was not born with a soulmate mark like most, which made her believe she didn't have a soulmate. When she meets Chat Noir she gets her mark, but it's a picture of a black cat instead of a name. Adrien subsequently gets a ladybug on his back.
- The short film The String is an original work based on this type of work. It's about a girl who doesn't have a Red String of Fate like everyone else. She eventually finds her soulmate who turns out to be a woman.
- Pn F Soulmates is a take on the powers variant, set in one where various powers are gained once you meet your soulmate, such as being unable to drown.
- Steven Universe: I Can't Believe Dumbledore Died is an Amethyst/Peridot fic of the "the first words you say to your soulmate are written on your arm" variety. Peridot unfortunately has "Man, I can't believe Dumbledore died." on her arm, spoiling her to the twist and leading to several uncomfortable Summers in long sleeves due to not wanting to spoil anyone else.