As part of writing up your application, please check the
character directory to find out if there are characters from that fandom already on the island. If there are, please contact the players via the e-mail address listed for the character, to inform them that you're applying a character from their canon.
This applies even if you're bringing in a character from an alternate universe or version of the story; if current FH characters would recognize your new character, their players need a heads-up.
If you're trying to go undercover as the player of the new character, contacting those players via a separate e-mail address set up for the character is fine. Other players don't have to know who's playing someone from their canon. You're not asking for permission to apply this character - just letting them know that it's happening. Any further discussion between you and the other player(s) is completely voluntary -- though it can certainly be very helpful in working out backstories and how the characters might affect each other.
About sharing backstories - that's one place where you do need permission. Fandom High allows only one version of each character, but different characters from the same canon don't have to come from the same timeline. If you wish your characters to share a timeline -- the non-canon life events that got them to Fandom High -- you must have the other player's agreement.
So it works like this:
If Jane Doe is a senior at Fandom High, and someone wants to play Bob Doe, her six-years-older brother, Bob's prospective player just needs to let Jane's player know that she's going to be applying for Bob. New-character Bob could come in as a freshman and be younger than his little sister! He just came from an alternate timeline, and left a wee Jane 2.0 behind him at home.
If, however, Bob's player wants Bob to be the same six-years-older Bob that Jane knows and loves, who came to Fandom because he missed his little sister and so he's getting a job as a teacher at her school, then both players have to agree to share that backstory.
Please let us know on your character application that you've checked into these things, if they apply. There's a Notes field you can use, or you're welcome to include the information elsewhere in the application if you find a more appropriate spot for it!