Since there wasn't any English walkthrough/ending list on Steam, I decided to make one, in the case there is people like me, that want to see all endings and achieve 100% CG or just want to know how to find a specific ending.

Disclaimer: This was made with the help from the JP Guide[sagaoz.net]made by Fool.

This VN has a total of 16 endings, being the recommended order for the character endings:
Sorane/Rikuno > Sara > Michiru 1 >Makina 1 > Makina 2> Tsumugi > Haina > Chisha > Michiru 2 [True End].
This walkthrough was designed from my playthrough and with the help from Fool's guide, while trying to avoid repeated scenes, see every scene/CG, and taking in mind the flow of the story.
If you don't like to follow a specific route order or are just after some endings, bellow the walkthrough there's an ending list, each one with the choices that leads to them.

It's important to mention that some of the endings, and choices to get them, can only be seen after achieving some previous endings. For example: if you are in your 1st playthrough, you won't be able to get the Sorane/Rikuno Ending [END 6]. To unlock it, you'll first need to see one of the 6 available endings (END 1, 2, 3, 4, 10, 14). You can see the endings you've got, and can get, in the EXTRA MODE*.

• *(EXTRA MODE is bugged, to fix it, see this thread).
  
• This guide works with both versions (+18 and All Ages).
  
• ~ Choices that may or may not appear. ~ They depend if you've seen a specific ending. If they appear select them, if not, just ignore them.

　 　
► Save 01
● It’s weird. Find it out.
► Save 02
● Come closer.

➽ Load Save 02
● Just leave.

➽ Load Save 01
● Life is precious. Just accept it.
► Save 03
● Go to Takuma.
~ Talk to Haina. ~
~ It’s just an illusion… calm down… ~

➽ Load Save 03
● Go to Takuma.
► Save 04
● Talk to Haina.
● It’s not an illusion… I also…

➽ Load Save 04
● Don’t talk to Haina
~ Ask the twins. ~
► Save 05
● Sorane [To see Sorane Scene]
➽ Load Save 05
● Rikuno [To see Rikuno Scene]

➽ Load Save 04
● Don’t talk to Haina
● Asking Sara.

➽ Load Save 03
● Don’t go to Takuma.
~ Have a rest in the room. ~
► Save 06
● Accept what Michiru said.
► Save 07
● Help Michiru.

➽ Load Save 07
● Help Chisha.

➽ Load Save 07
● Do something else I can do.
~ Study with Chisha. ~

➽ Load Save 07
● Do something else I can do.
► Save 08
● Refuse Chisha’s proposal.
~ It’s just an illusion. I’m too tired. ~

➽ Load Save 08
● Refuse Chisha’s proposal.
● …You’re right, Makina is…

➽ Load Save 06
● Accept the dream.
~ Ignore Tsumugi ~

➽ Load Save 06
● Accept the dream.
● Open the door.

➽ Load Save 06
● Accept the memory and hatred.
► Save 09
● Accept everything and live here.

➽ Load Save 09
● Pursue the above result while search other roads.
► Save 10
● Tell Chisha the truth.

➽ Load Save 10
● Say nothing.

Here are listed all the endings and choices for those who don't want to follow a walkthrough or just want to get some specific endings. And like the JP guide, I decided to divide the Endings List per "Scenario":

• 1st "Scenario"
  If you haven't got any ending before in your save file and it's your 1st playthrough, you can only get one of the 6 Endings available (END 1, 2, 3, 4, 10, 14).
  
• 2nd "Scenario"
  Unlocks after getting any Ending in the 1st "Scenario" & lets you access 4 new Endings (END 5, 6, 11, 12), plus all endings previously available.
  
• 3rd "Scenario"
  Unlocks after getting any Ending in the 2nd "Scenario" & lets you access 4 new Endings (END 7, 8, 9, 13), plus all endings previously available. (However END 13 can only be seen after completing END 12)
  
• 4th "Scenario"
  Unlocks after getting any Ending in the 3rd "Scenario" & lets you access 2 new Endings (END 15, 16), plus all endings previously available.

In your 1st playthrough you'll get one of this endings.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept the dream.
~ Ignore Tsumugi ~

Chapter 2
● It’s weird. Find it out.
● Come closer.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Go to Takuma.
~ Talk to Haina ~
~ It’s just an illusion… calm down… ~

Chapter 2
● It’s weird. Find it out.
● Just leave.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept what Michiru said.
Chapter 5
● Help Michiru.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Tell Haina that "I'm fine" to put her at ease. ~
● Accept what Michiru said.
Chapter 5
● Do something else I can do.
~ Study with Chisha. ~


Available after seeing at least one of the endings from the 1st "Scenario".

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Go to Takuma.
● Talk to Haina
● It’s not an illusion… I also…

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Go to Takuma.
● Don’t talk to Haina
~ Ask the twins. ~
● Sorane [For Sorane scene] or ● Rikuno [For Rikuno scene]

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept what Michiru said.
Chapter 5
● Help Chisha.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept what Michiru said.
Chapter 5
● Do something else I can do.
● Refuse Chisha’s proposal.
~ It’s just an illusion. I’m too tired. ~


Available after seeing at least one of the endings from the 2nd "Scenario", except END 13, this is only available after seeing END 12.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Go to Takuma.
● Don’t talk to Haina
● Asking Sara.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Tell Haina that "I'm fine" to put her at ease. ~
● Accept the memory and hatred.
● Accept everything and live here.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept the dream.
● Open the door.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept what Michiru said.
Chapter 5
● Do something else I can do.
● Refuse Chisha’s proposal.
● …You’re right, Makina is…


Available after seeing at least one of the endings from the 3rd "Scenario".

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept the memory and hatred.
● Pursue the above result while search other roads.
● Tell Chisha the truth.

Chapter 2
● Life is precious. Just accept it.
Chapter 3
● Don’t go to Takuma.
Chapter 4
~ Have a rest in the room. ~
● Accept the memory and hatred.
● Pursue the above result while search other roads.
● Say nothing.

Any questions, or mistakes I might have made, feel free to leave a comment.

Changelog:
24-02-2021: Reorganized things a little bit. Some typos fixed.
04-01-2022: Small arrangements to the text.

Thanks for reading the guide!