There are a number of Achievements, most of which are tied into the ending. Here are the requirements:
– Get each house to 100 (or Zealous, not sure which) and you will get the Befriend House achievement for the respective house.
– Uncover all 60 traits (difficult to do) by inquiring and focusing on characters who don’t have traits. This may be easier to do in a game where your focus is the achievement and not so much actually winning, although in order to get that far you may end up winning anyway.
Tips: You’ll want to run multiple characters with unrevealed traits as much as possible, and avoid using characters who are already revealed. Also, don’t sacrifice someone unless you’ve seen their traits, or else you’ll be locked out.
– Kill everyone in a single household is easy enough, although I suspect it’ll be difficult to win the game in that scenario.
Tips: Luckily 2 solo uses of a house are enough to make them not mad at you anymore, so you can keep killing them off one after another if you’d like as long as you keep all your other bars up in the meanwhile. You get 12 kills in total (4 per year) and there are only 6 members per household.
– The endings are all based off the result at the end of the final winter. Should any of your 5 tenets be in the negative upon this time, you’ll receive the ending for that tenet. On the other hand, if they’re all met and all the houses are happy (be careful about who you sacrifice as not to either change the threshold line or upset a family too much) then your God will rise. You may or may not need to wipe out all the Major Vice characters to achieve this.
RUMOR: It’s also theorized that even if you make it to the end if you haven’t found the remaining Major Sinner for your God that they’re asking to have sacrificed, you will get the ending for whatever tenet that sin is.