Rules of Writing in another writers Dimensions

[Tfmonkey]

I don't know if this is a thing or I am just over thinking this. Are there rules of using someone's story idea to write a story of your own in?

Theres an old writer named Robert who wrote "The baby hotel" stories and I want to write using the same content just different stories in that world. Do I need permission from the writer to do so?

[Cute_Kitten]

It's generally best to ask the author if they minded. One example is the Diaper Dimension by Princess Pottypants, and she's given her blessing for writers to use her world.  Another case I know of is someone wrote a sequel to another writer's original story and universe without asking, and that original writer, when they found out, really was not happy about it- I believe the story ended up getting taken down (it's been a hot minute, I don't fully remember). 

Now, if the author of the series you want to write fanfiction of is not around or has not been active for a very long time (I'm talking at least several years) and there's no way to get in contact with them, then I'd assume it would be okay to go ahead and write.  If this turns out to be the case, I recommend putting an author's note saying you tried to contact the original writer but were unable to do so.  Also, give credit! "My story is inspired by/ based off of/ set in X universe by Y author", or something along those lines.  Just give the original creator credit where credit is due for created worlds, characters, etc. 

[willnotwill]

I agree with Kitten.  It's best in a community like this to ask first.     Legally, there's nothing that stops you from writing as long as you're not copying or transforming the story someone else has written (or the characters rise to the level of being used as trademarks).

I've allowed others to write chapters into the middle of my stories.   If they want to develop the characters or situations into their own stories, by and large I'm OK with that, though I prefer to be asked.   There's one story line I'd rather reserve to myself.    I've also written chapters into other people's situations here.   Some of the threads have evolved into something akin to chapter long role plays.