is this the one? i forget how i got it, but i believe it has to do with the hinterlands expansion. mostly it has to do with the cemetery, it has a number of different ways that can play out in the last day, but it could also be the scene you return to the colonel state after doing the burial task.
Oh! Yah Purification is the one I'm missing. And the cemetery was just the hint I needed to solve it!!
Spoilers obviously
But talk to the Skinned Tapir God, and do his questline. Go to the non fiction section of the library. On the last day, go to the Cemetery!
Thanks to this, I was able to unlock the achievement. Then things turn differently better when meet the sister in the church beforehand, and when you go to the pond and get the Shed scene. Adds a friendlier dialogue and fear to P
I did Second Church > Skinned Tapir quest > non-fiction > shed > cemetery
