Factum Amoris by Lenore.

Slash.

I read this one a while back, when I had just started reading fanfic for SPN, to see if I could see what it was all about. At the time, I hadn’t liked the story, thought the premise of an enchanted sod house that trapped kids to sacrifice them for the harvest was a bit stretching it. Then, after reading many, many fics, I realized the theme of “we have to do it to save you/me/each other” was quite common. To shorten that title, I’ll call it the sex to save theme. Not badly done here, and their reactions after seem sane in that they realize that it’s not quite right what they’re doing.