This is a short guide to how you get each of the three different endings including their outcome.
Ending 1 (good ending, Steam achievement: Peace)
To obtain this ending, you have to go for the good path in all three boss fights at the end of every chapter.
Chapter 1
Use the three green light music players in the battle against Despair then push the button, interact with the monster to save her.
Chapter 2
Lower the gas pressure by using the valves in the four courners till all four lights in the middle control panel are green, then pull the switch. Interact with Corruption to save him.
Chapter 3
Lower the three cages by pulling down the lewers. Wait in the middle till the fight ends after reacting to the creature’s attacks four times in a row. Interact with Pain to save him.
Outcome
In this ending you will be reunited with your family and find peace. On the battlefield you will learn how you’ve abandoned your brother in the barb wire and told your family that he died. Ultimately your family will accept that the person that returned was not a monster but actually your injured brother.
Ending 2 (bad ending, Steam achievement: Ad Infinitum)
To obtain this ending, you have to go for the evil path in all three boss fights at the end of every chapter.
Chapter 1
Use the three red light music players in the battle against Despair then push the button, interact with the monster to kill her. Alternatively you can just defeat her and wait while she is getting sucked into the void without finishing her. The outcome of the game will not change but this will give you a different achievement.
Chapter 2
Increase the gas pressure by using the valves in the four courners till all four lights in the middle control panel are red, then pull the switch. Interact with Corruption to either kill him immediately or wait till he dies on his own for a different achievement.
Chapter 3
Rise the three cages by pulling up the lewers. Wait in the middle till the fight ends after reacting to the creature’s attacks four times in a row. Interact with Pain to kill him or wait till he dies on his own for another achievement.
Outcome
In this ending you will find the dead bodies of all three members of your family, saying that you’ve killed them. The officer will reward you and send you back to the battlefield where you are seemingly trapped forever, in an infinite loop.
Ending 3 (worse ending, Steam achievement: Lost)
To obtain this ending, you have to mix your choices. This means that you have to kill 1-2 bosses and save 1-2 bosses. I saved the first two and killed the third one in my walkthrough but I assume that every other way will work just the same.
Outcome
In this ending you will find some of your family members’ dead bodies while the others got redeemed based on how you chose to end the boss fights. The officer will appear in the end and kill you, saying that there is no such a thing as a half victory. You will end up in an asylum, haunted by the monsters that represent your family members.