Chapter 1
Welcome to the nightmare
Start Chapter 1, story-related.

Room
You find the room in chapter 1
Right at the start of chapter 1, open the door to this room and enter it.

Chapter 2
We have arrived in the city
Start Chapter 2, story-related.

The White Notes
You found all the white notes in chapter 2
Self explanatory, (probably) story-related.

Red Keycard
Unlock the door with the keycard in chapter 2
Self explanatory, story related.

Broken Doll
You broke the doll
Once you used the red key card, go left inside the building instead of right. Go through the garbage bins and find the blue key on the ground. Go back outside, to the blue door. Inside you find the green key, so go to the green door and touch the doll inside.

Chapter 3
Inside the apartments
Start Chapter 3, story-related.

The buttons of the sanctuary
You solved the button puzzle in chapter 3
Self explanatory, story-related. Solution is from left to right: 1324.

The Mystery Chest
Solved the combination of the chest in chapter 3
Self explanatory, story-related. Code is: 529.

The light is on
You returned the power to the apartments in chapter 3
Self explanatory, story-related.

Chapter 4
Inside my apartment
Start Chapter 4, story-related.

Kimochi
You found your Waifu in the bathtub taking a shower in chapter 4
At the start of chapter 4, go left towards the laundry room to the closed door to the bathroom, might be story-related.

The numbers of your heart
You solved the numbers puzzle in chapter 4
Use the code to the key pad in your apartment, story-related. Code is: 9214 .

Don't watch the VHS
You watched the VHS in chapter 4
Self explanatory, story-related.

Now we will go to the secret chapter 4.1. To do that, in chapter 4 when the game wants you to go to sleep, instead go to the bathtub.

The 3 paintings
Complete the puzzle of the paintings
In Chapter 4.1 you need to find all three paintings and put them in the correct order in room 0.
The correct order is
X: Painting 1
Y: Painting 2
Z: Painting 3 .

??????? VHS ??????
The secret VHS
After solving the paintings puzzle in chapter 4.1 and getting the key, go back to where the chains were, next to the "A" sign. They will be gone, so follow the new path. At some point go straight instead of right to get back to Block B. Now go to room 9 and tak the VHS from the safe. Go back to your apartment and play it.

Alternative Ending
Hidden
After the new path behind the gone chains, go right at some point instead of straight. You will leave the apartment (chapter 4.2). Enter the building where you previously needed the red key card to enter and found the blue key inside. Go on top of it.

Now load a save from chapter 4 or select it via chapter select.

Chapter 5
Back to the nightmare
Start Chapter 5, story-related.

Hiding Room
You find the secret room in chapter 5
Early on in the chapter, there is a room on the left side.

The sacred buddhas
You placed the 4 buddhas on the altar in chapter 5
Self explanatory, story-related.

The entrance to the temple of the moon
You found the entrance to the temple in chapter 5
Just after the previous, turn around and use the newly found key, story-related.

Chapter 6
Is it the prison? or the temple of the moon?
Start Chapter 6, story-related.

The switches
You solved the puzzle of the switches in chapter 6
Solution is from left to right: 1 up, 2 down, 3 up.

The alarms
The other world is here in chapter 6
Once you reach the point where the alarm starts and the world changes to red, story-related.

Normal Ending
Hidden
In chapter 6, ignore the code pad, backtrack, use the "long door key" and go to Akane.

Load back a save from chapter 6.

The numbers on the door
You solved the door puzzle in chapter 6
This time you need to open the door with the code pad. Code is 12922 .

True Ending
Hidden
Just continue after the previous achievement.