>>3354772It comes from けつまんこ、けつ means ass and まんこ means pussy, so it's easy to see where the mistranslation comes from, but けつまんこ simply means anus.
I would assume it was first mistranslated in a trap doujin cause it kind of works in that scenario, but when you read a doujin where a girl bends over and says "use my ass-pussy", that should've triggered a red flag for the translator.
