It began, in 2013, with a “Warning!! :)” about sexual scenes and explicit language. It ended, just last week, with a mid-six figure book deal.

Yet another piece of salacious teen fan fiction is making the uncomfortable leap from blogosphere backwater to Barnes & Noble — but “After,” the three-volume tale of an 18-year-old’s torrid love affair with One Direction frontman Harry Styles, is something of a special case. It’s long been the marquee story on Wattpad, a self-publishing platform that hosted more than 32 million stories in 2013. And in that role, it’s been popular. Like mind-numbingly, head-scratchingly, wtf-inducingly popular.

Per Simon & Schuster, the publisher that bought the book, the three books in the “After” trilogy have already been read a combined 800 million times. For perspective, that is: (1) almost twice the number of Harry Potter books that have ever been sold, (2) roughly 1.5 times the number of Apple iPhones in existence and (3) two and a half times the population of the United States.

In other words, “After” isn’t the next “50 Shades of Grey.” It’s already eclipsed that paltry franchise several times over.

I won’t delve into the intricacies of why a book like “After” is popular — plenty was written about that phenomenon when “50 Shades” first came out three years ago, much of it very condescending. There’s a natural impulse to dismiss fan fiction, particularly fan fiction written by women. Granted, that criticism is often pretty fair: From what I’ve read of “After” (and I have admittedly not read the whole thing), the writing’s bad, the story’s trite, and the sex scenes evoke way more cringes than goosebumps. But the book’s pseudonymous 25-year-old author, Anna Todd, clearly gets her audience in a very profound, even intimate, way.

This, for instance, is a pivotal fight scene in book 1, chapter 66:

“You don’t believe that I love you?” He gasps.
“Of course not, how stupid do you think I am?” I spit, he stares at me for a second before he opens his mouth and closes it again.
“You’re right.” he says.
“You’re right, I don’t. I don’t love you, I was just adding to the drama of the whole thing.”

And these are some of the responses from readers:

I am crying I hate you Tessa!
So many feels this is not okay, okay?
WHY IS HE SO MEAN?! WHY CANT HE JUST STOP?! Bawling my eyes out right now

… okay, whoa.

That’s what makes fan fiction, particularly on platforms like Wattpad, so fascinating. Wattpad, which launched in 2006, markets itself as a “community of readers and writers” rather than a publishing platform — which is fair. Authors and fans have profile pages and private inboxes; books, released in serial installments, have hopping comment sections where readers can provide feedback on each dribble of plot.

Todd, the “After” author, has said she spends half her day writing and half her day interacting with fans; her most popular piece on Wattpad, after the “After” trilogy, is a 10-part interview in which she answered reader questions. (Sample inquiries: Where in Texas do you live? What’s your favorite nail polish color? Are you a Directioner?) She has more than 273,000 followers on Instagram, and 182,000 on Twitter. On both platforms, Todd frequently reposts fan art and comments from her readers.

Maybe that seems like so much adolescent drivel, but it represents a serious shift in the role of the writer — traditionally a remote, solitary artist with little time or attention for fans. On Wattpad, at least, writing becomes more social. More collaborative. More “of the Internet,” essentially, with all the egalitarian values that entails. To quote the publishing consultant Charles Melcher, “now that everyone’s been given permission to be creative, new ways of telling stories … are being invented.”

And that kind of approach has apparently paid off — in addition to Todd, Wattpad writers like Brittany Geragotelis (“Life’s a Witch”) and Ali Novak (“My Life With the Walter Boys”) have scored IRL book deals off their online work.

So try not to roll your eyes when you see “After” on physical bookshelves in November — or when the eventual, inevitable movie comes out. (Todd has already signed on with the talent agency UTA to represent the film rights.) This type of crowd-fomented erotica may not be for everybody, but it’s definitely attracted enough fans to revolutionize publishing. Maybe for the better.