I'm having a lot of fun using Perchance's AI Character Chat for story writing.
https://perchance.org/ai-character-chat. I actually like it far more than their actual story writer.
Pluses:
Free
Unlimited (both generations and content)
Has a memory editor (so you can put the AI back on track ones it eventually loses its mind)
Has lore entries (for adding background info)
reasonably coherent
all content gets saved automatically
Minuses:
Doesn't do well with any more than 3 characters
doesn't have any advanced re-write options, like expand/describe/summerize
the ai behind it feels mediocre
Interesting:
Since it is character based, you can create a character that is a 'world class erotic fiction writer'. Define the writer to your tastes, they can like what you like -and hate what you hate. Alternatively, you can put a few characters from your story as AI chat characters & have them interact to create the story. I've also made a brainstormer. She generates ideas and asks questions about the story. Good for turning a premise into a rough outline.