The game is a little rough around the edges, but I really like the concept and story! Here's my playthrough for anyone interested:
Somebody else already made a quick walkthrough on the different ritual outcomes, but I wanted to dig deeper and I managed to approximate how the mechanics work because it's not really spelled out to you.
So, from what I can gather, the 4 endings are based on Octia's hidden stress meter and whether or not the ritual succeeds.
Here are the correct items for the ritual:
- Salt/Chalk (either will work)
- White Candles
- Carnations/Lock of Hair (having any or both will work)
- Container/Vial (either will work)
- Soap
- Eyeball
Failing/skipping any of the steps will fail the ritual (choosing to pause and return to the ritual is fine though).
The other variable is stress which is increased by doing certain actions:
- Interacting with specific spots near Aria (choose "No" when prompted to begin the ritual)
- The blood pool near her right hand
- The maggot near her right knee
- The top of her head above her missing eye
- Killing the goldfish (seems like it only increases stress if you choose to kill it at the first opportunity)
- Picking up the carnations in the vase
- Cutting Octia with the knife to collect blood in the container
- Drawing the ritual circle with salt AFTER Octia cut herself with the knife
- Using the spray to clean the Aria (will fail the ritual)
- Skipping the step to restore Aria's eyeball (will fail the ritual)
Notably, increasing stress enough will slightly change Octia's sprite.
The flashback cutscenes will also play no matter what ending you get though, so you just need to go through the game four times to get the whole backstory (which is a strange design choice to me, but what do I know?).