A trope that tends to be found in multiple fandoms I've come across is the soulmate fic.
While there are many different kinds of soulmate fics, they do tend to overlap a bit. But I have read some pretty unique takes on the trope, and I thought I'd share the basics of the most popular versions and the most unique ones I've seen.
1. Soul marks
This is by far the most popular type of soulmate fanfiction, and it actually can be broken down into three subcategories of soul marks: a soulmate's name, a soulmate's first words, or a design either shared or complemented by a soulmate.
Soul marks are tattoos and a person can be born with theirs or they can develop at a certain age that varies depending on the author's decision.
With a soulmate's name fanfic, it is pretty straightforward: People have tattoos of their soulmate's name—either just their first name or their full name—usually in their soulmate's handwriting, which for someone whose handwriting has changed many times over the years is a bit iffy for me, but whatever.
This type of soulmate fic is pretty popular for "Teen Wolf" Sterek writers because Stiles' first name was unknown for so long that it made for a fun take on the trope.
For a first word's fic, a person will have the first words their soulmate will say to them tattooed on their body somewhere—in some fics, every person's tattoo location is the same, and in some, it varies—again, usually in the person's handwriting.
It can be a fun chance for authors to make their characters suffer with ridiculous, embarrassing or super-common first words, like in one of my favorite WinterShieldShock fics. Darcy has a bad pickup line as one of her soul marks, so she greets everyone she meets with a bad pickup line as payback for whoever her soulmate is. Steve hears about this from his fellow Avengers who met Darcy before him, and decides to greet her with one as well, and low and behold, their pickup lines match. This brings to mind the "which came first, the chicken or the egg" question (if Darcy didn't have a pickup line soul mark, she wouldn't be greeting everyone with pickup lines, and Steve wouldn't have greeted her with his own, causing her soul mark), but that's probably too complicated a question for a cute and funny fic.
I'm also a big fan of the Gallavich soul words fic in which Mickey doesn't have soul words and goes his whole life thinking he doesn't have a soulmate before he meets Ian, who is mute.
In the third type of common soul mark fics, people have tattoos of an image or design that can either match their soulmate's exactly or complement the soulmate's design. The latter was an especially popular type of fic for One Direction Larry writers because of the number of tattoos both Louis and Harry have. Both boys have a handful of nautical-themed tattoos, so authors tended to write that Louis' compass was a complementary soul mark to Harry's anchor or ship.
If I had to compare (and I do because I'm making myself), out of the three, I think I've come across more first words soulmate fics.
Similar to soul mark fics, for soul timers, people have a tattoo on them—either when they are born or that appear at a certain age—with a timer that counts down to the exact moment they will meet their soulmate.
An issue that is brought up in more than a few timer fanfics in which the tattoos appear later in life is that the characters have already met their soulmates by then, and when the tattoo appears, it doesn't have any time on it. This leaves the characters having to figure out who in their lives could be their soulmate.
Timer fics can vary in two other main ways: The timers always stay clicking down without otherwise changing, or the timers change depending on certain decisions the characters make in their lives. So, if a character decides to take the bus instead of walking to work, their timer may change from an hour left until they meet their soulmate to three years.
For both soul timers and soul mark fics, if a soulmate dies before meeting their other half, the living soulmate's mark can fade, disappear or scar over, letting them know that they won't meet their soulmate. Dark, I know.
3. Dream sharing
I must admit, I haven't read a dream-sharing soulmate fic in a very long time, but they do exist.
These are pretty much exactly what they sound like. Soulmates share dreams. Usually, like real dreams, soul dreams are vague and the characters cannot tell exactly what their soulmate looks or sounds like. Until they meet in the real world, the dreams will continue so the soulmates can get to know each other.
4. Soul connection
I read a Gallavich soulmate fic once wherein everyone is connected by an incorporeal red string to their soulmate. It attaches to each half's pinky and cannot be seen by anyone else. The string will get shorter and glow brighter the closer the soulmates get to one another.
5. Imaginary soul friend (?)
Not sure how to title this one, but anyway.
In one of the more unique Larry fics I read long ago—it's been taken off AO3 since then, sorry—everyone has a sort of imaginary friend/ghost-like being/astral projection of their soulmate who follows them around and becomes more conscious the closer a person is to meeting their soulmate.
So in the beginning, the shade (I'm going to call it a shade from now on) is mostly invisible, can't speak and basically just floats around its person. But as the time they are going to meet their soulmate draws nearer, they become more physical—able to do things like poke their person or move items around—and their shape becomes more defined. Once the soulmates are about to meet, the shade becomes almost a mirror of the person's soulmate before disappearing once the soulmates touch.
These shades want the soulmates to meet, so they will push their people in the direction of their soulmates if they can.
Have you read any unique soulmate fics that I didn't include? What's your favorite type of soulmate fic? What's the most interesting take on a soul mark fic you've come across?