The ending you get depends on your decisions during several key moments, as well as your interaction with the girls. The game has 10 endings in total, though the paths toward them vary in length.

The Memory of White Day achievement for getting all endings actually requires you to get all 10 of them on each of 5 difficulties. Thankfully, you don't need to beat the game 50 times.

To my knowledge, if you set up the correct dialogue options and save at strategic points throughout the game, you can get all ten endings while:

• Completing Main Building 1 only once, instead of ten times
  
• Completing Main Building 2 only twice, instead of eight times
  
• Completing New Building only twice, instead of eight times
  
• Completing the Auditorium fight five times instead of eight
  
• Sadly, you'll still need to complete Ji-Min's section twice in full

This guide will list all 10 endings for reference, and then provide the optimal path through the game that will allow you to get all endings with minimal repetition.

Truth
So-Young's good ending, as well as the canon ending to the game.

• Be nice to So-Young, agree with whatever she says and don't annoy her.
  
• Mention her diary and the paranormal happenings when available.
  
• After picking up the Wood Token, ignore Sung-A and investigate the sound of crying.
  
• After using the Earth Talisman, ignore Sung-A and follow So-Young.
  
• In the new building, give So-Young a can of coffee and then her diary.
  
• In the Labyrinth, pick up the unconscious So-Young and escape together with her.

If you follow this route but manage to irritate So-Young or fumble your dialogue choices, you will end up with ending I instead. Refer to the optimal path section below for a foolproof walkthrough.

Forgive Me
So-Young's bad ending.

• After using the Earth Talisman, ignore Sung-A and follow So-Young.
  
• In the Labyrinth, leave So-Young behind.

Friendship
So-Young's neutral ending.

• After using the Earth Talisman, ignore Sung-A and follow So-Young.
  
• In the Labyrinth, pick up the unconscious So-Young and escape together with her.

Dangerous Pleasure
Sung-A's "good" ending.

• Be nice to Sung-A, agree with whatever she says and don't annoy her.
  
• After picking up the Wood Token, choose to follow Sung-A.
  
• After using the Earth Talisman, ignore So-Young and stay behind to talk to Sung-A.
  
• In the new building, drop the Backmasked Tape into the complaint mailbox.
  
• In the auditorium, after talking to Ji-Hyeon, choose to go look for Sung-A.

If you follow this route but manage to irritate Sung-A or fumble your dialogue choices, you will end up with ending E instead. Refer to the optimal path section below for a foolproof walkthrough.

Hypocrisy
Sung-A's neutral ending.

• After using the Earth Talisman, ignore So-Young and stay behind to talk to Sung-A.
  
• In the auditorium, after talking to Ji-Hyeon, choose to go look for Sung-A.

Sincerity
Ji-Hyeon's good ending.

• Be nice to Ji-Hyeon, comfort her and don't annoy her.
  
• After picking up the Wood Token, choose to follow Sung-A.
  
• After using the Earth Talisman, ignore So-Young and stay behind to talk to Sung-A.
  
• In the auditorium, after talking to Ji-Hyeon, choose to tend to her ankle.

If you follow this route but manage to irritate Ji-Hyeon or fumble your dialogue choices, you will end up with ending A instead. Refer to the optimal path section below for a foolproof walkthrough.

Tired of Love
Ji-Hyeon's neutral ending.

• After using the Earth Talisman, ignore So-Young and stay behind to talk to Sung-A.
  
• In the auditorium, after talking to Ji-Hyeon, choose to tend to her ankle.

Death
Bad ending.


Obtained by dying in any way at any point.

You Are Mine
Ji-Min's good ending.

• Be mean to Ji-Min in main building one, then ask about her doodles.
  
• Find all ten doodles before picking up the Wood Token.
  
• After picking up the Wood Token, ignore Sung-A and investigate the sound of crying.
  
• In the principal's office, check the third monitor, then go straight to 3F biology lab.
  
• After rescuing Ji-Min, be nice to her.

As you take control of Ji-Min, she will remark that she hopes to see Hee-Min soon.

If you follow this route but manage to irritate Ji-Min or fumble your dialogue choices, you will end up with ending M instead. Refer to the optimal path section below for a foolproof walkthrough.

Hidden Love
Ji-Min's neutral ending.

• Find all ten doodles before picking up the Wood Token.
  
• After picking up the Wood Token, ignore Sung-A and investigate the sound of crying.
  
• In the principal's office, check the third monitor, then go straight to 3F biology lab.
  
• After rescuing Ji-Min, choose the most annoying options.

As you take control of Ji-Min, she will remark that she's worried.

This section will detail how to get all the endings with as little repetition as possible, using strategic saving and reloading.

The guide assumes you're already familiar with the game progression. If you're having difficulty with puzzles or don't know where to go, please refer to this helpful walkthrough by Stef.

Remember that Ji-Min only appears on subsequent playthroughs after you complete the game once, on a difficulty no lower than Normal, and with any of So-Young's endings (W, H or I.)
If you don't have her unlocked yet, ignore the sections relating to her and don't bother with her wall doodles. The guide will mention an opportunity to make a save that you can reload after unlocking her to get her endings.

Note: Since saves are normally disabled on the Hell difficulty, I recommend using Sui's hack[github.com] to enable them. Otherwise you'll have to play the game on Hell 10 times from start to finish, or tamper with save files manually. The hack also contains some fixes and QoL additions.

• Meeting Sung-A and Ji-Hyeon:
  ► Sorry, I didn't know you guys were here.
  ◄ I'm Hee-Min Lee.
  ► Uh... I left something here.
  ◄ Okay. What am I going to help you with?
  
  
• In gameplay sections when the girls are around, make sure not to annoy them. Don't interact with them, don't make them wait, don't bump into them and push them around, don't look up their skirts, etc. If you do that, their affection will lower, and this can lock you out of certain endings.
  
  
• After following Sung-A to the toilet:
  ◄ Ok, just what kind of help do you need in here?
  ◄ Alright.
  
  
• You will need a Can of Coffee for a later event in the New Building. The earliest and easiest way to obtain it is while fetching the ladder for Sung-A. Check to the right of the vending machine for a coin on the ground, then buy a coffee.
  
  
• Talking to Ji-Hyeon after running from the janitor:
  ◄ Punished? Is that what YOU call punishment?
  ◄ No... I don't think I do. Sorry.
  ► I'm just running some errands.
  ◄ I've got you.
  
  
• If you don't have Ji-Min unlocked yet (refer to the start of this section), you can make a separate save after talking to Ji-Hyeon but before entering the 2F Hallway.
  After you unlock Ji-Min, reload the save you made here to access her route and endings.
  
  
• Meeting Ji-Min:
  ► Can you step aside so that I can go in the classroom?
  ► You're blocking my way!
  ► I haven't seen you before either.
  ◄ Do you like doodling?
  
  
• Meeting So-Young:
  ◄ I wanted to return your diary...
  ◄ Yeah... I saw Ji-Hyeon, too.
  
  
• After defeating the tree monster and before picking up the Wood Token, you'll need to find all ten of Ji-Min's wall doodles to access her route. Here's a handy map by Shino Takadora. It can be done earlier, but not later.

• After finding all doodles and before picking up the Wood Token, ❗make a separate save file❗ and don't overwrite it. This will be our main save file from which all routes are accessible. It will be referred to as Save 1.
  
  
• After picking up the Wood Token, conversation with Sung-A:
  ◆ Either option
  ◆ Either option
  ◆ Either option
  ► [Go to where the sound is coming from.]
  
  
• So-Young shows up:
  ◄ Are you alright? Are you hurt?
  ◄ There was a piece of wood that looked like a talisman. All I did was put that piece in place...
  
  
• After talking to So-Young, walk towards the stairwell on the right to find Ji-Min:
  ◄ Aren't you the one who's chasing after So-Young?
  ► You are the one who's been stalking So-Young. Why don't you go ask yourself...?

• In the Headmaster's Office, check the second and then the third monitor. You will see Ji-Min in the Biology Lab.

• Before picking up janitor's key from 1F Faculty Room, ❗make a separate save file❗
  This save will let us reach both of Ji-Min's endings. It will be referred to as Save 2-JM.
  
  
• Do not pick up janitor's key yet, as it will lock you out from Ji-Min's route. Instead, go straight to 4F Biology Lab.
  
  
• Rescuing Ji-Min:
  ◄ Are you okay? Are you hurt anywhere?
  ► I don't know if you know this already... but all the exits are locked...
  ► Fine by me...
  
  
• As you first take control of Ji-Min, she will remark:
  🗯 Hey... we can meet soon, right?
  This confirms you're locked into ending J. Continue playing normally.
  
  Jasmine ✔
  
  
• Reload Save 2-JM. Again, go straight to 4F Biology Lab, then rescue Ji-Min:
  ► There's a nice smell...
  ◄ Okay... Go ahead...
  ◄ Well... Okay. Whatever...
  
  
• As you take control of Ji-Min, she will now remark:
  🗯 Whew... I'm worried... In every way...
  This means you're locked into ending M. Continue playing normally.
  
  Marguerite ✔
  
  
• Reload Save 2-JM for the last time. It won't be needed afterwards and can be safely overwritten.
  
  
• Go to 1F Faculty Office and grab the key. So-Young will appear:
  ◄ No, I didn't leave because I'm worried about you.
  
  
• On the staircase, So-Young asks if you believe in ghosts:
  ◄ Yeah. I do now...
  
  
• After unlocking the Faculty Office:
  ► Do you have any proof?
  
  
• After using the Earth Token to open the door to New Building:
  ◄ [Go after So-Young.]

• Just as you enter:
  ◄ Are you worried about Ji-Hyeon?
  ◄ I... I just want to help you.
  ◄ Well, I'm glad I'm being helpful at least.
  
  
• In the Faculty Lounge, when So-Young sits down in a chair saying she's tired, make sure you have a Can of Coffee on you and interact with her to offer it. If you don't have one, there's a vending machine in the hallway.
  
  
• Afterwards, interact with her again:
  ◄ [Give back the diary.]
  ◄ I'm Hee-Min Lee. It's nice to meet you.
  
  
• Go down to the first floor:
  ◄ Hey, you okay? Are you hurt?
  
  
• Go up to the second floor and unlock the door and the end of the hallway. Don't take too long and don't bother So-Young by interacting with her, etc. Afterwards, continue playing normally until you get the Blue Keycard.
  
  
• After obtaining the Blue Keycard, So-Young appears:
  ► Why did she kill herself?
  
  
• Continue normally until you enter the Auditorium.

• After grabbing the Fire Token but before using it or talking to So-Young,❗make a separate save file❗
  This one will be used for endings W, H and I. It will be referred to as Save 3-WHI.
  
  
• Talking to So-Young here is actually not mandatory. If you do, don't interact with her further. Use the Fire Token and complete the Labyrinth.
  
  
• At the end of Labyrinth, pick So-Young up and escape together with her.
  
  White Chrysanthemum ✔
  
  
• Reload Save 3-WHI and use the Fire Token. At the end of the Labyrinth, leave So-Young behind.
  
  Hyacinth ✔
  
  
• Reload Save 3-WHI for the last time. After talking to So-Young, continue interacting with her to annoy her until you she says:
  🗯 Ugh... I'm so tired of you.
  
  
• Use the Fire Token, complete the Labyrinth, pick So-Young up and escape together.
  
  Ivy ✔
  
  
• Since you got endings W, H and I, Save 3-WHI is no longer needed and can be overwritten.
  
  
• Load Save 1.

• After picking up the Wood Token, conversation with Sung-A:
  ◄ So-Young's gone...
  ► Uh... that is, um...
  ◄ Really? Is So-Young really like that?
  ◄ [Go after Sung-A.]
  
  
• After catching up to Sung-A:
  ◄ Yeah. I heard it, too.
  ◄ So-Young had a sister?
  ◄ Yeah. She's just making it harder on herself.
  ◄ Not necessarily. So-Young could be in trouble for all we know.

• After picking up the Backmasked Tape, Sung-A shows up:
  ◄ I've been waiting for you.
  
  
• Running into Ji-Hyeon in the Science Supply Room:
  ◄ Don't be scared, it's just me.
  ► Ji-Hyeon, are you okay?
  
  
• Remember to not interact with Ji-Hyeon further, not to bump into her, etc.
  
  
• After using the Earth Token on the door:
  ► [Talk to Sung-A.]
  ◄ No, it's just a coincidence.
  ◄ Do you believe in ghosts now?
  ◄ She ran away... alone.

• After Sung-A saves you from the janitor:
  ► Thanks for saving me.
  ◄ What makes you so sure?
  ► No, I believe you.
  
  
• Running into Ji-Hyeon in the Library:
  ◄ Have some faith. I promise I'll find the way out.
  
  
• After playing the Backmasked Tape and talking to the teacher, take the tape out of the cassette player and keep it.
  
  
• After defeating Eu-Min, conversation with Sung-A:
  ◄ Yeah, I'm fine.
  ► I think she went crazy after her daughter died.
  

• After defeating Eun-Mi but before moving to the Auditorium, ❗make a separate save file❗
  This one will be used to roll back after ending T. It will be referred to as Save 4-T.
  
  
• On the fourth floor of the main hall, right in front of the stairs, there's a complaint mailbox. Put the Backmasked Tape into it, then continue to the Auditorium.

• After extinguishing the fire, conversation with Ji-Hyeon:
  ◆ Either option
  ◆ Either option
  ► [Go find Sung-A.]
  
  Tuberose ✔
  
  
• Reload Save 4-T.

• This time, ignore the mailbox.
  
  
• You're going to need an Emergency Kit for an upcoming event. There is one at the base of the stairs om the first floor in the main hall of the New Building. Another one can be found in the Auditorium in the Girls' Shower Room during the fight.
  
  
• Proceed to the Auditorium.

• After turning on the lights and unlocking the double doors, but before entering the court and starting the timed event, ❗make a separate save file❗
  This one will let us reach endings E, D and A. It will be referred to as Save 5-EDA. You can save it over Save 4-T since that one is no longer needed.
  
  
• After extinguishing the fire, conversation with Ji-Hyeon:
  ◆ Either option
  ◆ Either option
  ► [Go find Sung-A.]
  
  Ebony ✔
  
  
• Reload Save 5-EDA.
  
  
• After extinguishing the fire, conversation with Ji-Hyeon:
  ► Are you okay? Did you get hurt?
  ► It's not safe for you to be alone.
  ◄ [Tend to Ji-Hyeon's ankle.]
  
  Dandelion ✔
  
  
• Reload Save 5-EDA.
  
  
• After extinguishing the fire, conversation with Ji-Hyeon:
  ◄ I think it's all over now.
  ◄ Are you sure you'll be okay on your own?
  ◄ [Tend to Ji-Hyeon's ankle.]
  
  Althaea ✔
  
  
• Finally, if you haven't yet, load any save file and die in any way.
  
  Yew ✔

Thank you for reading.

I am not entirely sure that every single listed dialogue option is 100% mandatory, but I can confirm that as of v1.0.10, following this guide as it is written will get you the endings you need.

If you spot a mistake or know of a better strategy, please leave a comment and I will update the guide and credit you.

If you found my guide useful, consider buying me a can of coke on donatty[donatty.com]
or boosty[boosty.to]
Cheers!