Let's start off with Lucifer's ending since it's frequently asked.

To achieve Lucifer's ending, you have to get the bad endings for Lior, Renan, and Shilo during either chapters 4 or 5.

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Hidden Ending

 The hidden ending takes place during the beginning if Belial fails to make a pact with Shilo, Lior, and Renan.

During each human love interests' Chapter 1, select the following:

 Shilo Chapter 1 /  pick the choice  You're the same as every other human, just more vulnerable.

Lior Chapter 1 /  pick the choice  Because you looked like an easy target.

Renan Chapter 1 /  pick the choice You're right. That was my plan.

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Now to unlock all the CGs...

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Lucifer's CGs

CG 1 - Auto unlocks during the Prologue

CG 2 - Auto unlocks after Chapter 4

CG 3 - Continuously talk to Lucifer in Belial's room until you exhaust all of the options

CG 4 - Achieve Lucifer's Ending. How to unlock this ending is written above.

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Shilo's CGs

CG 1 - Auto unlocks during the Shilo's Chapter 1 after you pick the choice Because I could tell that you're different.

CG 2 - Unlocks during the Shilo's Chapter 2 after you pick the choice Let him continue

CG 3 - Unlocks during the Shilo's Chapter 3 after you pick the choice Is this form more appealing to you?

CG 4 and 5- Auto unlocks during the Shilo's Chapter 4 

Avoid Shilo's Bad Ending during Chapter 4 by selecting the choice Death by accident.

CG 6 - Auto unlocks during the Shilo's Chapter 5

Avoid Shilo's Bad Ending during Chapter 4 by selecting the choice But don't you feel bad for the kid?

CG 7 - (Good Ending2) Unlocks during the Shilo's Chapter 6 after you pick the choice You should reconcile with your brother.

CG 8 and 9 - (Good Ending1) Unlocks during the Shilo's Chapter 6 after you pick the choice You should think about what you want.

CG 10 - (Bad Ending1) Unlocks during the Shilo's Chapter 4 after you pick the choice Death by your own hands.

CG 11 - (Bad Ending2) Unlocks during the Shilo's Chapter 5 after you pick the choice He's as annoying as his father.

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Lior's CGs

CG 1 and 2 - Auto unlocks during the Lior's Chapter 1 after you pick the choice Because I wanted to help you.

CG 3 - Unlocks during the Lior's Chapter 2 after you pick the choice Mess with him a little

CG 4 - Unlocks during the Lior's Chapter 3 after you pick the choice Show him what to do

CG 5 and 6- Auto unlocks during the Lior's Chapter 4 

Avoid Lior's Bad Ending during Chapter 4 by selecting the choice Step in

Avoid Lior's Bad Ending during Chapter 5 by selecting the choice I will still stay with you.

CG 7 - Unlocks during the Lior's Chapter 5 after you pick the choice I will still stay with you.

CG 8 and 9 - (Good Ending2) Unlocks during the Lior's Chapter 6 after you pick the choice Exorcism.

CG 10 - (Good Ending1) Unlocks during the Lior's Chapter 6 after you pick the choice Confront your mother.

CG 11 - (Bad Ending1) Unlocks during the Lior's Chapter 4 after you pick the choice Let it play out

CG 12 - (Bad Ending2) Unlocks during the Lior's Chapter 5 after you pick the choice I'm going to leave you.

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Renan's CGs

CG 1 - Auto unlocks during the Renan's Chapter 1 after you pick the choice No, I chose you specifically for a reason.

CG 2 - Unlocks during the Renan's Chapter 2 after you pick the choice Help him calm down

CG 3- Auto unlocks during the Renan's Chapter 3

CG 4 - Unlocks during the Renan's Chapter 3 after you pick the choice Tease him

CG 5 and 6 - Auto unlocks during the Renan's Chapter4

Avoid Renan's Bad Ending during Chapter 4 by selecting the choice Remember to be the bigger person.

CG 7 - Auto unlocks during the Renan's Chapter5

Avoid Renan's Bad Ending during Chapter 5 by selecting the choice This might be serious.

CG 8 - (Good Ending2) Unlocks during the Renan's Chapter 6 after you pick the choice I want you to continue following your dreams.

CG 9 - (Good Ending2) Unlocks during the Renan's Chapter 6 after you pick the choice I will protect you no matter the path you choose.

CG 11 - (Bad Ending1) Unlocks during the Renan's Chapter 4 after you pick the choice You should hurt him.

CG 11 - (Bad Ending2) Unlocks during the Renan's Chapter 5 after you pick the choice Don't worry about it.

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Okay! That should be it! Let me know if I'm missing something!