Tag description a character has sex with an independent copy of themselves, through time travel, cloning, magic, or any other means
note i feel like the "copy" is both a flawed word for the description and a word that is needed to separate selfcest from more exotic forms of masturbation like "portal onaholes" that just go back to the character. having a whole "copy" that acts separate from the character feels necessary to the spirit of selfcest.