AI fanfiction: how to write fanfic with an AI writer

To write fanfiction with AI, do not ask for "a fic about" two characters. Tell it the fandom and which version of it, the characters and how each one talks, where in canon the story sits, the premise, and the tone and length you want. Then treat what comes back as a rough draft. The AI supplies sentences quickly. You supply what fans read for: the voices, the canon details, and the reason this story needs telling.

Be ready for one thing above all. An AI may not know your canon, especially if it is recent or small, and it will write as if it does.

What AI is good and bad at in fanfic

It helps with:

getting a premise onto the page when you are stuck at the first line;
trying the same scene from a different point of view;
a list of what-ifs to pick from, such as ten ways a canon event could have gone differently;
the linking scenes between the ones you care about;
notes on your own draft.

It is weak at:

Canon. It mixes up events, shifts the timeline and invents backstory. With recent releases and small fandoms it may know almost nothing and bluff.
Voices. Everyone drifts towards the same polite, articulate speaker. The sarcastic one turns kind. The quiet one starts making speeches.
Conflict. Arguments get settled in three lines, and characters say their feelings out loud as if reading from a list.
Length. Over many chapters it forgets what happened earlier and repeats itself.

What to tell it

The fandom and the version. Books, show or game, and which season or instalment.
Where it sits in canon. After which event. Say whether it follows canon, breaks from it at a named point, or is an alternate universe.
The characters. Two lines each on how they speak and what they would never do. Do not trust it to know.
The premise. One or two sentences.
The kind of fic. Missing scene, hurt and comfort, fluff, angst, humour, a case.
Point of view, tense and length.
What to avoid. No speeches about feelings, no summary at the end, nobody out of character.
"Only the story."

A prompt to copy and fill in:

Write a [kind of fic] of about [length] words for [fandom and version]. It takes place [where in canon]. Characters: [name], who [how they talk, what they would never do]; [name], who [the same]. Premise: [one or two sentences]. Keep to canon: change nothing that happens in it and invent no new backstory. [Point of view], past tense, [tone]. Nobody says their feelings outright. End on an action or a line of dialogue, not a summary. Only the story.

A worked example

Here it is filled in for an old fandom, so the details can be checked against the books:

Write a missing-scene fic of about 600 words for the Sherlock Holmes stories, the original books. It takes place on the evening after a case ends. Characters: Holmes, who speaks in clipped, exact sentences, turns thanks aside and never admits he was worried; Watson, who narrates, is warm and a little dry, and notices more than Holmes thinks. Premise: Watson finds that Holmes has kept every one of his published accounts and written in the margins. First person, past tense, quiet and fond. Nobody says their feelings outright. End on a line of dialogue. Only the story.

Lines like these are what you are hoping for:

"You have corrected my spelling," I said.
"Twice. You are otherwise reliable on spelling." He did not look up from the fire. "It is the facts you take liberties with."
I turned the page. In the margin, beside my account of the moor, he had written a single word: accurate.

Holmes stays sharp and Watson stays dry. Nobody says "I value you", and the margin note says it for them. If the draft has Holmes thanking Watson warmly for his friendship, that is the voice drifting, and it is the part to rewrite.

Fix the draft

Read it once for each of these.

Canon. Check every name, place and event against the source or a fan wiki. Do not take the draft's word for anything.
Voice. Cover the names. Can you still tell who is speaking?
Character. Would they really say that? Cut the apologies and the neat self-knowledge that canon never gave them.
The ending. If the last paragraph sums up what it all meant, cut it.
The scene people came for. The confession, the reunion, the fight. Write that one yourself.

Ask for changes to one part at a time: "rewrite her lines only, shorter and ruder". Starting over throws away what was working. How to write a short story has more on scenes, dialogue and endings.

Longer fics

Work chapter by chapter, never the whole thing at once. Keep two documents and paste the relevant parts in each time:

A character sheet. How each one talks, what they want, and the facts that must not change.
The story so far. A few lines for each finished chapter.

Without them, the AI will bring back a character you wrote out, or forget who knows the secret. Write the plan yourself. An AI's idea of a plot is the most expected one. How to write a book with AI goes through the method for long work.

Posting it honestly

Read the rules where you post. Archives and communities differ on AI-assisted work, and the rules change. Some ask for a tag and some do not allow it.
Say so. A tag or an author's note is enough. Fandom runs on trust, and readers who feel tricked do not come back.
Leave other fans' work alone. Do not paste someone's fic into an AI to copy their style or carry on their story without asking them.
Keep it free. The characters belong to their creators, and the custom in fandom is that fic is shared and not sold. Whether you may do more than that is a legal question this page cannot answer.

Doing it with Hemmingway

The fanfiction generator asks for the fandom, the characters and your premise, and opens Hemmingway with those filled in. The story is written in the chat, where you can ask for changes. Read it against canon and rewrite what is off before you post it anywhere.

Hemmingway-1 is better at short pieces than long ones, so one-shots and missing scenes suit it. For long chaptered fics, larger story models scored higher in StoryBench, our own story test: Fable 5 Max and GLM-5.3 came above Hemmingway-1, which sits level with Kimi K3. The full results. It writes best in English, it may not know recent canon, and it can get a detail wrong while sounding sure. In the app, Memory can hold the facts you do not want to repeat, and you can read and change every line of it.

Try Hemmingway Download the app

Common questions

Can AI write fanfiction?

Yes. It can write a complete fic from a premise in seconds. How good it is depends on what you tell it about canon and the characters, and on how much you edit afterwards.

What is the best AI fanfiction generator?

It depends on the length. For one-shots and short scenes, a model built for short writing that sounds like a person does well. For long chaptered stories, the large story models scored higher in our own tests. We have not run a test of fanfiction on its own.

Does AI know my fandom?

It may know old and very popular ones in outline, and get the details wrong. It may know nothing of a recent or small one and invent things. Either way, give it the facts it needs in the prompt and check the draft against the source.

Is it okay to post AI-written fanfiction?

Check the rules of the archive or community first, because they differ and they change. Where it is allowed, tag it or say so in a note. Readers mostly mind being misled.

How do I keep characters in character with AI?

Describe how each one speaks and what they would never do, in two lines each, and say "nobody says their feelings outright". Then read the dialogue with the names covered and rewrite any line that could belong to anyone.

Is there a free AI fanfiction writer?

Hemmingway has a free trial with no card needed, and the fanfiction generator opens it with your fandom and premise filled in. Plans are on the pricing page.

Writing fanfiction with AI