***** SPOILER WARNING *****
***** Significant plot details about the different types of endings follow. ******
***** SPOILER WARNING *****
***** Significant plot details about the different types of endings follow. ******
(I only take partly credit for this solution. Is is nearly entirely based on the Catherine-Wiki, catherinethegame.wikia.com)
There are 8 different endings to Catherine, based on whether you choose Katherine or Catherine, and where your karma meter is at the end of the game.
During Stage 9, you are asked four different questions. The answer to the first question doesn't affect anything (!). The answers to question 2 and 3 influence what question 4 is, and all the questions together (along with your karma meter) change what ending you get. (!)
Every different ending will get you an achievement.
For ease, you can save your game at the Landing of Stage 9-2, and reload it multiple times answering different ways to get alternate endings. A new game is necessary to shift your karma meter from Order (Law) to Chaos or Neutral (!). Neutral (exactly in the middle!) being, of course, the most difficult one to get.
An easy way to keep your karma at neutral during a second playthrough is to completely ignore all phone texts from Catherine and Katherine. At that point, the major thing that changes your karma is the confessional questions, which you can alternate between Law and Chaos each level. Always keep an eye on the meter, and just adjust your answer accordingly, to get it in the middle. If you don't speek to anyone, never (and never have to answer questions), the confessional is the only thing than changes your meter. So alternate every stage and you're good to go.
Once you've completed the game and start a new one, you are allowed to skip any puzzle sections that you received a gold prize on, allowing you to quickly obtain all endings. You can do this by pressing "Start" during the puzzle you wish to skip, and choosing "Skip."
The three questions of night 9 are:
1) Would you risk everything to get your lover back?
Of course! / Maybe not everything... (doesn't influence the ending)
2) Do you wish for a peaceful life?
Yes / No
3) Do you wish for the excitement of chaos?
Yes / No
The endings can be achieved depending on your karma meter. To get a specific ending, answer the questions like this:
Katherine True (Maximum Law)
2)Yes ... 3) No ... 4) I'm ready
Katherine Good (Heavily Law)
2)Yes ... 3) Yes ... 4) Peaceful Days
2)Yes ... 3) Yes ... 4) Not really
2)Yes ... 3) No ... 4) Yes
Katherine Bad (Heavily Chaos)
2)Yes ... 3) Yes ... 4) Peaceful Days
2)Yes ... 3) No ... 4) No
Catherine True (Max Chaos)
2)No ... 3) Yes ... 4) Yes
Catherine Good (Heavily Chaos)
2)Yes ... 3) Yes ... 4) Chaotic Excitement
2)Yes ... 3) No ... 4) Yes
2)No ... 3) Yes ... 4) No
Catherine Bad (Heavily Law)
2)Yes ... 3) Yes ... 4) Chaotic Excitement
2)No ... 3) Yes ... 4) No
Freedom Good (Heavily Either)
2)No ... 3) No ... 4) Yes
Freedom True (Middle) (!)
2)No ... 3) No ... 4) Yes
P.S. It's been reported that if you are at max Chaos or Order at the first landing of Stage 6, there is just enough time to get the meter into the middle (by answering all questions Law/Chaos appropriately) to get the Freedom endings by the end. This should save quite a bit of time in replaying.