I've been posting on this site for a while now, and throughout my time here I occasionally see these romance rps based around people having a mark on them that connects them to their soul mate. It's not as though it's a huge trend but there's enough of a pattern for these rps to peak my curiosity because, despite taking place in multiple sections and being created by multiple users, they seem to have an established set of rules they tend to follow. People are marked, they're fated to fall in love with the one that shares there mark, if one of the pair dies the mark goes grey etc etc...

What I'm wondering is what is the source for these rps? Is this a standard RP type on the internet? Was there an anime or fantasy novel that used this as a premise? And if anyone has played in them, did it go well and stay compelling?

Stories like the one you've mentioned are a staple of b-grade romance from Japan.

While it is a familiar "trope" I have not personally watched/read/etc much of it. I did watch a pg-13/mecha/lesbian anime featuring that as a premise, but I can't remember the name. It was underwhelming on a lot of levels, but I think I understand why people tend to use it in RP frequently.

Essentially, it's an easy way to get two characters into a relationship with minimal effort and maximum angst. If the characters have zero chemistry or hate each other, they will still hang out with each other to fulfill the prophecy, find their one and only, etc. In fact, not meshing well is better because it amps up the conflict. This also guides the characters away from less abusive relationships because they don't have the "mark." Even if you're not into all of that crap, it's an easy hook up. You don't need to think of an excuse for these characters to come together beyond "oh look, they have 「THE MARK」! Guess I'd better get to know them so that we can pork."

So while I don't know when it started online, I know it's been going around Japan for a while. But I think the reason it caught on is because it cuts to the "romantic" part instantly while bypassing all that "annoying" stuff like discovering each other. And for those who love angst, it's a low effort way to make sure a toxic relationship lasts well beyond its shelf life. But like all things RP, how good it is depends on how much effort you and everyone involved with it puts into it.

You could bring it back to ye-olde-English with the Gypsies and palm reading to see what your life path will be. I don't think it's an anime exclusive thing, but it sure does happen a lot in anime themed RPs.

As a writing piece, it helps add that destiny aspect that some roleplays may lack. People do find it hard to write motivations so having a physical mark just makes it easier.

I'm not convinced you can point to any one source and go "that's where this comes from and they're all inspired by that." From where I'm standing it just seems like the most conducive way to format a soulmate situation. Just seems to be one of those pervasive things, kinda like those dystopian stories where a dome covers an area and everyone inside turn against each other, anything set in an academy of any kind or anything featuring a "chosen one." Broad concepts and tropes kinda become public domain after they make the rounds a few times, if that makes sense.

From a practical standpoint, it would be difficult to have some kind of soulmate-style, fated-to-be-together type setting without some kind of identifying feature such as a mark. Obviously you could work something out without it, but what can I say? People like the trope!