It's likely about sex, as it says mate with all spirits. I'm not actually 100% sure tho. I am still a bit confused, if you are suggesting I use the debug console, I know I can do that and was looking for a legitimate way to get the achievement, hence why I asked for a strategy if someone knew how to do it :)
If you or someone does know a way to legitimately get the achievement, I'd love to hear it. I am also quite interested in your claim about being able to mate with all spirits in one day (assuming it doesn't use the console)