The introduction is pretty straightforward, just making your way straight through the school until you come across this white board.
Click on each magnet to rotate them until you form an “A” on the signboard.

Continue forward until you encounter a cutscene and leads you to a room full of bookshelves with a “A” built with a tower of books.
Head to the far left bookshelf and interact with the books to find a hidden pack of cigarettes and then head towards the tower of books in the centre of the room.

Enter the 3rd toilet cubicle from the left and pick up the Calvin’s phone on the toilet. After the cutscene open the door of the cubicle next door to find a corridor through the wall.
Walk to the end of the corridor to trigger the short cutscene and return back to the main school toilet area.

After returning to the school toilet area you will encounter another cutscene, walk towards the mirror and then head back to the toilet stalls to trigger the next sequence.
Continue with the on-screen prompts until you arrive at the next scene.

Head towards the pet carrier on the cabinet in front and grab the sparrow coin to the right of it (you’ll be needing a lot of them later, but don’t worry if you already went past this part and missed this one)

Explore the home and interact with this odd eyeball alarm clock on the table to trigger a short cutscene.
Walk back into the living room, turn left and enter the room on the right.
Sometimes the door might still be closed. If you encounter that, you could interact with the door then walk away and walk back again, that should trigger the door opening.

Now enter the room and read the note in the far end of the room to trigger the next scene.

Now let me preface this, at this point in the game we have completed the initial section of the game and from this point on the game becomes more of a semi open exploration area divided by different floors. There will be several different ways that you can play the game from this point but I will focus on the key steps required to complete the game (Sorry achievement hunters).

Okay, back to the guide. Follow down the corridor until you reach a more open area, walk forward until you see a small ghostly girl and walk towards her to trigger the cutscene.

Now remember those coins we were talking about earlier, there are several of them here and this is where you can find them in no particular order.

On a stone bench just to your right when you enter this first open area.
Inside these joss paper burners, there is an empty one in the same room but you can usually find coins in them.
and the last coin in this room will be from this puzzle on the left side of the room.
The note on the table should give you an idea of how solve it but here’s the answer for those of you who are bad at algebra.

O has 6 blue and 4 red marbles, A has 4 blue and 1 green marble and C has 1 blue and 5 red marbles.

Now grab the Sparrow Coin from the drawer on the right of the puzzle and head to the next area past the metal gate here to the next open area.
Now that you are entering the next open area, walk forward and grab the 2 Sparrow Coins off the table straight ahead.
Once you’ve grabbed those, head to the right of the room where you can see an open door with a glowing red electric box blocked by a wall of hair. Next to it you should see a green bin, head over to it and grab the Old Paper Cutter.

Head over to this gate and cut the rope using the Old Paper Cutter to enter the next room.
Head all the way into Olivia’s home and head to the wok in the kitchen and grab another Sparrow Coin.
Now head into the room on the right and pick up the diary in the cupboard just up ahead.
Head towards the window and interact with the object on the glass panel and head back out of the room to answer the telephone just outside.
Head out of the apartment and make your way back to the first open area where you say the ghost girl, a new zone should have been unlock on the right.
Make your way inside into the sewers and remember to grab another Sparrow Coin just on the left before continuing to your right.
Keep following the pipes and you will eventually reach this segment.
Take the right most path and walk all the way to the end where you will encounter a series of tunnels that you can to crouch walk to get through.
There is another Sparrow Coin here as well so you know the drill.
Now just continue following the linear path up until you acquire the basketball. If you’re stuck here, you just need to crouch under the arms to get to the end.
Now that you’ve acquired the basketball you can right click to summon it and use it as a weapon or a tool for some puzzles. For the tutorial you just have to toss and hit some hands with the ball.

Now make your way back to this room for the next puzzle.
The finger all the way on the right is a reset switch and the other 5 fingers with bloody tips represent a hand.

Use your basketball to knock out the levers so that the “hand” is point a middle finger. So just leave the middle lever up.

Turn around and the door to the carousel should have been opened. Jump on and interact to head to the next zone.

In this interactive cutscene, you need need find and pass the ball back to Olivia 3 Times. Because of the static effect, it can be difficult to see sometimes but the ball generally rolls pretty far away from the post.

Follow along the path until you encounter the ghost girl again here.
Before moving forward there will be a path behind you that will lead you to another Sparrow Coin and an Alarm Clock that is needed for one of the achievements.

Now continue on the original path and pick up Dream Word Piece 2/2 and continue to the next room where you should find Dream Word Piece 1/2 on the ground. Continue to the next room and pick up the Sparrow Coin off the side table then head to the wall up ahead.
Combine the 2 Dream Word Pieces in your inventory using the + sign to create Dream Word. Then insert it into the interactable on the wall.

Turn back and head through the tunnel that has now appeared.
Continue down the tunnel and hit the board with the basketball to exit the tunnel. (You will continue to see the smiley face as a motif for using the basketball) Also note that your crouch does not reset when you fall down so remember to un-crouch yourself so you can move at normal speed.
You will encounter an entity blocking the way forward, just use your handy dandy basketball to get rid of it and continue forward and head to the barber shop area.

In this area you need to find 3 Mannequin heads to place on the dolls in the center of the room to unlock the next area.

Let’s start with the room on the left. Knock out another hairball and pick up the Sparrow Coin inside the room. Now we’re onto the next puzzle.
Just arrange the circles in order from empty to half black.

Head to the opposite corridor and pick up another Sparrow Coin before opening the gate to some stairs. Look up and you should see 2 giant pairs of scissors. Hit them with your basketball to trigger them to close and grab the Mannequin heads from them. The hit box be weird so try to aim it at the center of the scissors, that’s where I generally found success.
Head back to the room and place all 3 Mannequin heads. Then proceed down the newly unlocked corridor and pick up a key item Paper Scissors before heading back down the corridor.

After the cutscene you should have now been transported back to the initial HDB Floor 5 area. Remember that open door covered with hair? Head back to that location and throw your basketball at the electric panel inside. This should open the shutters just next to you and access to the main elevator.
By default you should have access to Floor 5 (the current floor) as well as Floor 2. For now let’s head to Floor 2.

Walk down the corridor and you should see this room on the right. You can crouch under and pick up the Recorder Head.
There are also several Sparrow Coins here to collect, the first of which is just resting on the barricade next to the room where you got the recorder.
Head to the end of the corridor to grab another Sparrow Coin.
And another one on this table here.
Smack down another hairball blocking your way and head into the room ahead and on your right you’ll find another Sparrow Coin.
Continue on the other side of the room to trigger a cutscene with ghost girl and then proceed to interact with the furnace and burn the Paper Scissors in your inventory. Now you should have access to the room near the elevator.

But before that we will make a short detour to the other entrance on the right where you will pick up a phone call and you guessed it, another Sparrow Coin. Now you can head back to the door that was just unlocked.
Surprise, you’ve just encountered the first “mini-boss” encounter. You have to hit Calvin with the basketball at least 3 times, with the final one in the room with the furnace once the door closes behind Calvin.

You may sometimes feel like you are immediately killed, but you actually regain control over your character around when he starts swinging his trophy. When you hit him with the ball he will be flinched for a short time but he will raise his arms up like this after he recovers and prevents him from being hit for a short period of time.
After defeating Calvin, head back to the unlocked room and you should see a gacha machine and another furnace. Head all the way inside the room and enter a side room on the left to grab another Sparrow Coin.

At this point you should have at least 19 coins if you’ve followed this guide closely. Use 11 coins in the gacha machine to get the Floor 3 button for the elevator.
After you’ve attained the Floor 3 button, head back to the elevator and head to Floor 3.

After arriving, just head straight to trigger the cutscene. Then move forward and grab another Sparrow Coin (don’t worry another 4 coins and we will be done).
Continue down the corridor on the right until you find a red table. Grab the Sleeping Pill off the table and head into the door just next to it to trigger the next scene.
After being abducted into the holding cell, turn towards the wall and hit the bottom edge that is flickering slightly with the basketball. This should reveal a hole that you can crouch through.

Move this cabinet out of the way to access the door to escape.
From this point, Olivia’s dad will constantly patrol the area and pursue you if you are spotted. You can hide in the bins to lose him but you have to make sure you do it while outside his line of sight or he will still catch you. The area has also opened up so you can explore further into the floor.

You will notice a burning mannequin head on a robe in a cage.

You will need to use the basketball to knock the unlit mannequin heads into the lit one so that all 3 mannequin heads are on fire. Once you’ve done it, you’ll get rewarded with a Sparrow Coin.

Continue into the door leading to a small corridor and you should come across this blue partition here. Behind it you will find another Sparrow Coin and Journal Page.
Head out the door on the other end and you should see this table below with another Sleeping Pill for you to collect.
Just behind this spot there will be a room which is accessed only via crouching. Head in and there should be a service lift that can be called down by hitting the panel on the side with the basketball. Lower the lift and interact with the button to raise you to the upper floor.

Now that you are at the upper floor, head to the room next door and pick up the Recorder Body from the body in the middle of the room. There is also another Sparrow Coin on the left.
Proceed to combine the Recorder Head and Recorder Body together. You should probably practice this here while it’s safe by using the recorder. If you’ve done it right, you should hear yourself playing Twinkle Twinkle Little Star.
Now that’ you’ve got some practice, head back to this room and play the song while you’re inside the room. BEWARE, your playing will trigger the boss if he is nearby so make sure to wait until he’s gone further away. You will know you’re in range of the puzzle when the light in the room turns green.
You will now get another 3 Sleeping Pills which should give you a total of 5 Sleeping Pills. Find Olivia’s Dad’s room and fill his pill bottle with all 5 Sleeping Pills.
After the cutscene you will be able to move freely around the level but remember to grab the a Room Key from his waist to access the next area.
Use the Room Key to open the door just behind you and continue to head further into the rooms. On the right you should see a note and a locked box. The answer on the note is fake and you need to first solve the riddle on the wall all the way inside.
There are 4 sides rooms here, each with a garbage chute. Here's the riddle for easy reference.

Hair Falls And Fades,
Skin Stings And Tears,
Flesh Steams And Melts
And Bone Burns To Ashes

If you assign each room a number while facing this riddle from left to right with 1 to 4. The the solution to this puzzle is 2341.

You should here a cling nearby, head to the front of the room and you should see that a whole series of colored gloves have spawned.
This part is pretty straight forward, just count the number of gloves on each of the hangars and you will get your combination 2363.

Now head over to the lockbox and enter the combination. Align the numbers with the red indicator line and once the numbers are in place remember to click one more time to open the box and trigger the next cutscene and head back to where the riddle was.
Listen to what Olivia has to say and follow her instructions to get the object from her. For some reason you have to pick up the object inside of the chute in room 2 so make sure you grab it before you leave. Now you will have the Lift Button #4.
Now return back to the elevator and head to the 4th Floor.

Head to the left and grab a Sparrow Coin (by now you should have 13 in your inventory and any additional coins you pick up from this point will just be a good to have)

Crouch under the right most shutter that says Out of Order and pass through the crack in the wall.
Continue inside and crouch under this to continue forward. You should see another Red Electric Panel that you need to hit with your basketball.
For this chase sequence you can hit the spirit with the basketball to flinch it but it will become less effective the second time as it will require multiple hits. So just run and make your way back to the crack in the wall to end this sequence.

This shutter at the opposite end of the room should now be open.
There is another 2 Sparrow Coins in this room if you missed out on any of the previous one. But continue to head inward until you see a basketball court.

In this area there are 3 spots marked on the ground with Xs. Stand inside each one and throw your basketball through the hoop to open one of the shuttered rooms on the right. Just take note that you will trigger a scene transition if you complete all 3. But don’t worry you will be able to come back to collect any items later.

Continue into the level until you reach a dark room. Turn right and you should see a room with 2 screens of light on the wall. Then head to the opposite end of the room and interact with the light on the wall.
Head to the top left and then follow the trail of dead birds to reach the end.

Proceed along until you encounter this room. Each of the side rooms has a clue for 1 of the answers on the board.
Grab onto the projector and use it’s light to see shadows in each room. In each room one of the objects will have a bird on it. That will be the correct answer for each room.

The answer is: - J AI 1 and the room in the opposite end of the corridor should now be open, head there and trigger the next cutscene.

After the chase sequence continue along until you find another light projection on the wall.
For this puzzle wait in the center for a second until you can see a bird flying across the screen. Follow it’s direction 4 times and you will complete this puzzle.

Continue forward and walk to the edge of the giant hole in the room to trigger the next cutscene.
Avoid the hands and pick up the falling feathers to ascend up to the top to finish this area.
In this next section you will mainly be platforming by picking up feathers that will make you float for a short period of time. Make your way to the end of the platforming section.
You should end up in this corridor here and you can proceed to the end to trigger the cutscene.
Once the cutscene is done, walk forward into the hands and proceed into the second classroom on the left and interact with the projector to trigger the cutscene and return back to the basketball court.

Now that you are back, there is another 5 Sparrow Coins in the rooms behind the shutters but remember to pick up the Lantern Candle key item from this room here.
At this point, you can head back to Floor 2 or Floor 5’s gacha machine to deposit the remaining Sparrow Coins to get the Lift Button #1. Now head back to the elevator and head to Floor 1.

This segment is fairly linear, so just make your way to the end of the corridor until you encounter a telephone which you need to interact with.
Backtrack slightly until you are cut off by the building collapse and then head back to the room with the telephone to trigger a cutscene. Continue forward through the hole in the wall to enter a Lift Shaft, walk to the end and pick up the Paper Shoe key item.
After the cutscene, head all the way back up the lift shaft and enter the elevator at the end to return to HDB Floor 2. Now head over to the furnace and burn the Paper Shoe and return to this room which has now been cleared. Pick up the Paper Lantern key item on the table inside.
After that head over to this room with the tic tac toe board on the same floor.
The hint to the puzzle is on the wall just next to it but here’s the solution of the puzzle is as follows:

XOX
OXO
XOX

Continue past the now open gate beside you until you enter a room that catches on fire when you walk in. To stop the fire you have to avoid the flames as much as possible and get to the stove at the back of the room and turn it off by spam clicking.
Go through the door on the right of the stove and enter the next room. For this room you will need to do the same as the previous room by turning off 2 stoves but now you will also be chased by a spirit while doing so.

You have the option of stalling him with the basketball or by kicking over barrels in their direction to give you time to turn off the stoves. One stove is just on your right and the other is in the middle far end of the room.

Once done, proceed through the door on the left most side of the room and open the shutters by hitting the electric panel again.
You should enter a room that seems to be a kitchen with another furnace on the right. Combine the Paper Lantern with the Lantern Candle to make a Lit Paper Lantern. Use the Lit Paper Lantern in the furnace to proceed.

The room behind you should now be open. For this next puzzle you will need to input buttons in the elevator based on a certain combination. The hint for the puzzle is on the wall just outside the lift.
The 5 button should already be lit so the solution is just 2341.

At this point you will be facing off with Olivia’s Dad. The battle is simple, you will not be fighting him directly but you will need to avoid him while activate all 4 Electric Panels around the level. At certain moments Olivia’s Dad will pick up pots on the ground and toss them at you, you will need to hide behind one of the lamp posts to avoid damage. But beware as you will only have 4 lamp posts available.

Make your way through the maze and be careful of the “hair balls” around the corners. After a short maze you should arrive at the mirror room.
You should see a faint ghostly figure of yourself in the left most mirror, mimic it’s movements along the mirror until you open the way to the next section. Continue along the maze until you reach this area and head towards the mirror at the end of the corridor.
You should find this room full of cracked mirrors just on the left of that corridor.
After a brief cutscene, you will need to use your basketball to break the mirrors with the flames on them to complete this puzzle.
Once complete, face the mirror in the middle of the room and then turn around and break the mirror behind you to proceed. Continue down the path until you abruptly get sent to another scene.

Travel through the hallway until you reach this interactable segment.
Walk through the wax and interact with the lantern on the statues. After the cutscene interact with the note on the lantern and be sent to the next segment.
Interact with the mannequin and the break the glass on the left to reveal a path forward.
In the next room, wait for the monologue to complete then break the glass on the right to proceed. I think you should get the drill by now so just keep doing the same thing until you reach the end of this section.

Now that you’re back to when you picked that not from the lantern, turn left and head to the next room.
Enter the room and head towards the door on the right and you should trigger the next scene. Olivia will grab you and force a choice on you, depending on your choices it can affect the ending that you receive. If you want the good ending, select the options where the heart on the scale is lighter like in the picture below.
Attack the animated mannequins and aim for the head to defeat them. Defeat all the mannequins to trigger the next part.
After the second dialogue with Olivia you will be facing off with 2 spirits concurrently. This segment can be frustrating as you will have to do this entire room again if you fail but here are some tips.

The primary objective is to burn both spirits with the fires in the barrels around the arena. However, due to the long animation if you only hit 1 it is likely that the other will kill you immediately once you have control of your character. You should try to stun them in a way that groups both of them up and then knock the barrel to burn both of them. Note that even though you hit both you need to do this twice to defeat both spirits.

Once you’ve completed the third dialogue with Olivia you can end the now open door to the next level.
For this battle you will need to knock out all 4 mannequin eyes on the boss. After hitting an eye, the boss will use it’s arms to defend itself, you will need to hit the middle fingers on those arms to lower them so that the eyes can be hit again. The boss primarily does 2 moves, one where he slams the middle of the arena and the other on the outer depending on where the player is standing.
After hitting all the eyes, the boss will fall down and you need to walk up close to trigger the short cutscene. Do this entire rotation 2 more times and you should be done with the battle. Just be careful that in the second rotation the boss also summons the mannequins to attack you.
You should now be in a fiery landscape, there is a path drawn out by the flames that you can follow. Continue until you reach this door, crouch under to get across.
You will encounter these large circular disks that are flying at you. Despite how it looks you can walk into them. You will have to stop moving when it is about to hit you otherwise it will send you back to the start of the puzzle.
For the second half, it is better to do it backwards so you can see the circles coming at you. Once you have reached the end, go through the door and find Olivia under the table amongst the flames to trigger the cutscene.

You will be prompted to click during this cutscene so look out for the mouse icon.
Once you reach the elevator shaft just walk to one of the corners and then continue watching cutscenes until the end of the game.

I hope this guide has been helpful for you, if there are any issues feel free to inform me and I will update the guided accordingly.