Does anyone know a one-shot where two young (elementary school?) girls say they want to marry each other, but when they get home it turns out their moms got married so they became sisters instead? Then there's a timeskip to when they're in highschool together and dating despite being stepsisters.
I was looking through the Pseudo-incest for this but I couldn't find it, so it might not have been tagged (I might've just missed it though). I think it was SFW, but I'm not sure.