In Chaos;Head, you have to deal with different types of triggers in order to change specific scenes:
Positive (left/green), negative (right/red), and neutral (no trigger/just proceed without triggering anything)

Note: This guide was tested on the regular Steam version; I didn't install any additional fan translation patch. So the dialogues I'm referring to came from the original Steam release.

This guide is based on the guide for the Japanese PS3 version of the “PSN Trophy Leaders” forum. https://psntrophyleaders.com/forums/forum/gaming/ps3imports-org/ps5-ps4-ps3-digital-and-physical-based-games/chaos-head-noah-ab/78069-chaos-head-noah-road-map
I have made some changes to match the Steam version and also added a few more details like dialogues etc.

In order to access the full game, you have to beat Route A first:

Chapter 1
Answer all three questions with "yes".

With Misumi in the class room: "I hated to disappoint Misumi when he was so excited, but I had no intention of going."
-> left trigger

With Nanami in Takumi's room: "There's nothing here but soda! You should keep some milk tea or something in stock!"
-> left trigger

With Yua across the street: "...!"
-> left trigger

With Yua in Takumi's room: "..."
-> left trigger

Yua's bag: "Wait..."
-> left trigger


Chapter 2

Sequence with the doctor: "The first doctor to look at me was an old man ..."
-> left trigger

Seira: "Wow, Takky! You hate going outside, but you still..."
-> left trigger

Fill out every point on the medical formular and proceed by pressing "ok".

The concert scene with FES: "-looked right at me."
-> right trigger

Takumi's room: "Hey, KnightHeart... I'm always watching you, you know."
-> right trigger


Chapter 3

At the street: "And then she really swung it!"
-> left trigger

With Misumi inside the school building: "FES didn't even look at him."
-> right trigger

Takumi's room: "Damn it... Not now."
-> right trigger

With Kozue in the class room: "Sure enough, there was a girl there."
-> left trigger

At the roof: "There were only five calls there."
-> left trigger

At the convenience store: "There was nobody."
-> left trigger


Chapter 4

With Rimi in the class room: "..."
-> left trigger

Sena sitting in the train: "Instead of the sword, the white chain was coiled up at her feet."
-> left trigger

At the computer booth: "The booth was tiny. Yua blocked the only exit."
-> right trigger

At the park: "The police..."
-> left trigger

At the underpass: "Still panting for breath, I looked over at FES."
-> left trigger


Chapter 5

In the class room: "For example..."
-> right trigger

With Rimi at the CD store: "put her hands on my shoulders."
-> left trigger

Takumi's room: "No, no, no. I was jumping to conclusions."
-> right trigger

Takumi's room, you'll see the door this time: "WHAT DID SHE JUST SAY?!!!!!"
-> right trigger

With Kozue at the lockers: "..."
-> left trigger


Chapter 6

Takumi's room, when chatting with Shougun: "I hung up the phone, disappointed."
-> right trigger

Outside with Sena: "It was you, wasn't it?"
-> left trigger

Takumi's room, you'll hear a phone: Whose... phone... was ringing?"
-> left trigger

You'll see a crowd: "Why are they all looking at me?"
-> Right trigger

Respond to the questions like this: Yes, yes, no, no, yes

A flying sword: "..."
-> left trigger


Chapter 7

With the nurse at the hospital: "But why this hospital, though?"
-> left trigger

At the class room: "I didn't have any reason to come to school anymore."
-> left trigger

With Kozue at the street: "About five minutes, nora."
-> right trigger

Kozue's Di-Sword: "It looked completely different than the ones Ayase and Sena had."
-> right trigger

With Sena and Kozue: "U-Um... You can have this."
-> left trigger


Chapter 8

Takumi's room, looking at the door: "Rimi asked me for the impossible as she sat down..."
-> left trigger

At the hospital room: "The room was small and simple in layout."
-> left trigger

At the hospital room, yes, again: "Gladiale... Now I remembered."
-> left trigger

With Rimi and Misumi at the hospital: "Tahaha. Aw, now I look like an idiot for trying to hide it."
-> right trigger

With Rimi at the roof: "Um..."
-> left trigger


Chapter 9

With Rimi: "There were at least four delusions synchronized there that night."
-> right trigger

Cars on the street: "Maybe I'd be better off dead. If I wasn't real, there was no point in being alive."
-> right trigger

Seira figure and poster: "But right now, Seira-tan was all I had."
-> left trigger

Takumi's room: "That voice..."
-> right trigger

Seira: "This is your second shot."
-> left trigger

This will unlock the “Silent Sky” ending and give you access to the full game. Be sure to check out tip 142 before starting a new game to earn an additional trophy.


Now it's time to start a new game:

Chapter 1
Answer all three questions with "no".

With Misumi in the class room: "I hated to disappoint Misumi when he was so excited, but I had no intention of going."
-> No trigger
You'll see a text on the blackboard. The scene then proceeds by showing you two doors, respond to the questions like this: No, No, Yes, Yes, No

With Nanami in Takumi's room: "There's nothing here but soda! You should keep some milk tea or something in stock!"
-> right trigger

With Yua across the street: "...!"
-> no trigger

With Yua in Takumi's room: "..."
-> right trigger

Yua's bag: "Wait..."
-> no trigger


Chapter 2

Sequence with the doctor: "The first doctor to look at me was an old man ..."
-> no trigger

Seira: "Wow, Takky! You hate going outside, but you still..."
-> no trigger

Leave the medical formular blank and proceed by pressing "ok".

The concert scene with FES: "-looked right at me."
-> left trigger

Takumi's room: "Hey, KnightHeart... I'm always watching you, you know."
-> left trigger


Chapter 3

At the street: "And then she really swung it!"
-> right trigger

With Misumi inside the school building: "FES didn't even look at him."
-> no trigger

Takumi's room: "Damn it... Not now."
-> left trigger

With Kozue in the class room: "Sure enough, there was a girl there."
-> right trigger

At the roof: "There were only five calls there."
-> right trigger

At the convenience store: "There was nobody."
-> no trigger


Chapter 4

With Rimi in the class room: "..."
-> no trigger

Sena sitting in the train: "Instead of the sword, the white chain was coiled up at her feet."
-> no trigger

At the computer booth: "The booth was tiny. Yua blocked the only exit."
-> no trigger

At the park: "The police..."
-> right trigger

At the underpass: "Still panting for breath, I looked over at FES."
-> right trigger


Chapter 5

In the class room: "For example..."
-> left trigger

With Rimi at the CD store: "put her hands on my shoulders."
-> no trigger

Takumi's room: "No, no, no. I was jumping to conclusions."
-> left trigger

Takumi's room, you'll see the door this time: "WHAT DID SHE JUST SAY?!!!!!"
-> no trigger

With Kozue at the lockers: "..."
-> right trigger


Chapter 6

Takumi's room, when chatting with Shougun: "I hung up the phone, disappointed."
-> left trigger

Outside with Sena: "It was you, wasn't it?"
-> no trigger

Takumi's room, you'll hear a phone: Whose... phone... was ringing?"
-> no trigger

You'll see a crowd: "Why are they all looking at me?"
-> no trigger

Respond to the questions like this: No, no, yes, no, yes

A flying sword: "..."
-> no trigger


Chapter 7

With the nurse at the hospital: "But why this hospital, though?"
-> right trigger

At the class room: "I didn't have any reason to come to school anymore."
-> no trigger

With Kozue at the street: "About five minutes, nora."
-> no trigger

Kozue's Di-Sword: "It looked completely different than the ones Ayase and Sena had."
-> no trigger

With Sena and Kozue: "U-Um... You can have this."
-> right trigger


Chapter 8

Takumi's room, looking at the door: "Rimi asked me for the impossible as she sat down..."
-> no trigger

At the hospital room: "The room was small and simple in layout."
-> no trigger

At the hospital room, yes, again: "Gladiale... Now I remembered."
-> right trigger

With Rimi and Misumi at the hospital: "Tahaha. Aw, now I look like an idiot for trying to hide it."
-> no trigger

With Rimi at the roof: "Um..."
-> no trigger


Chapter 9

With Rimi: "There were at least four delusions synchronized there that night."
-> no trigger

Cars on the street: "Maybe I'd be better off dead. If I wasn't real, there was no point in being alive."
-> no trigger

Seira figure and poster: "But right now, Seira-tan was all I had."
-> no trigger

Takumi's room: "That voice..."
-> left trigger

Seira: "This is your second shot."
-> no trigger

Make sure to check tip 142 again for another trophy. (Yes, there are two trophies related to this tip). You'll also unlock the "Crying Sky" ending.


It's time to start the 3rd playthrough:

Chapter 1
Answer all three questions with "yes".

With Misumi in the class room: "I hated to disappoint Misumi when he was so excited, but I had no intention of going."
-> left trigger
You'll see a text on the blackboard. The scene then proceeds by showing you two doors, respond to the questions like this: Yes, no, yes, no, yes

With Nanami in Takumi's room: "There's nothing here but soda! You should keep some milk tea or something in stock!"
-> no trigger

With Yua across the street: "...!"
-> right trigger

With Yua in Takumi's room: "..."
-> no trigger

Yua's bag: "Wait..."
-> right trigger


Chapter 2

Sequence with the doctor: "The first doctor to look at me was an old man ..."
-> right trigger

Seira: "Wow, Takky! You hate going outside, but you still..."
-> right trigger

Just hit "ok" when you receive the medical formular .

The concert scene with FES: "-looked right at me."
-> no trigger

Takumi's room: "Hey, KnightHeart... I'm always watching you, you know."
-> no trigger


Chapter 3

At the street: "And then she really swung it!"
-> no trigger

With Misumi inside the school building: "FES didn't even look at him."
-> left trigger

Takumi's room: "Damn it... Not now."
-> no trigger

With Kozue in the class room: "Sure enough, there was a girl there."
-> no trigger

At the roof: "There were only five calls there."
-> no trigger

At the convenience store: "There was nobody."
-> right trigger


Chapter 4

With Rimi in the class room: "..."
-> right trigger

Sena sitting in the train: "Instead of the sword, the white chain was coiled up at her feet."
-> right trigger

At the computer booth: "The booth was tiny. Yua blocked the only exit."
-> left trigger

At the park: "The police..."
-> no trigger

At the underpass: "Still panting for breath, I looked over at FES."
-> no trigger


Chapter 5

In the class room: "For example..."
-> no trigger

With Rimi at the CD store: "put her hands on my shoulders."
-> right trigger

Takumi's room: "No, no, no. I was jumping to conclusions."
-> no trigger

Takumi's room, you'll see the door this time: "WHAT DID SHE JUST SAY?!!!!!"
-> left trigger

With Kozue at the lockers: "..."
-> no trigger


Chapter 6

Takumi's room, when chatting with Shougun: "I hung up the phone, disappointed."
-> no trigger

Outside with Sena: "It was you, wasn't it?"
-> right trigger

Takumi's room, you'll hear a phone: Whose... phone... was ringing?"
-> right trigger

You'll see a crowd: "Why are they all looking at me?"
-> left trigger

Respond to the questions like this: Yes, yes, no, no, yes

A flying sword: "..."
-> right trigger


Chapter 7

With the nurse at the hospital: "But why this hospital, though?"
-> no trigger

At the class room: "I didn't have any reason to come to school anymore."
-> right trigger

With Kozue at the street: "About five minutes, nora."
-> left trigger

Kozue's Di-Sword: "It looked completely different than the ones Ayase and Sena had."
-> left trigger

With Sena and Kozue: "U-Um... You can have this."
-> none trigger


Chapter 8

Takumi's room, looking at the door: "Rimi asked me for the impossible as she sat down..."
-> right trigger

At the hospital room: "The room was small and simple in layout."
-> right trigger

At the hospital room, yes, again: "Gladiale... Now I remembered."
-> no trigger

With Rimi and Misumi at the hospital: "Tahaha. Aw, now I look like an idiot for trying to hide it."
-> left trigger

With Rimi at the roof: "Um..."
-> right trigger

This will unlock the "Anima Archetype" ending.

Chapter 1
Answer all three questions with "yes".

With Misumi in the class room: "I hated to disappoint Misumi when he was so excited, but I had no intention of going."
-> right trigger

With Nanami in Takumi's room: "There's nothing here but soda! You should keep some milk tea or something in stock!"
-> left trigger
The scene then proceeds by showing you two doors, respond to the questions like this: No, yes, no, yes, yes

From here don't use the left or right trigger. Just proceed without making any decision, this will also help with gathering all "neutral" triggers.

You'll unlock the ending "Daydream" after completing chapter 7.


Now it's time to unlock the remaining endings.

You should be able to select the necessary chapter directly from the main menu:
Continue > Shortcut

Make sure to use the "Don't Skip Unread" option, so you won't miss the new sequences.

Select chapter 9 "giga-lo-maniac" from the chapter select.

Chapter 9: giga-lo-maniac

With Rimi: "There were at least four delusions synchronized there that night."
-> left trigger

Cars on the street: "Maybe I'd be better off dead. If I wasn't real, there was no point in being alive."
-> left trigger

Seira figure and poster: "But right now, Seira-tan was all I had."
-> right trigger

Takumi's room: "That voice..."
-> no trigger

Seira: "This is your second shot."
-> right trigger

Select chapter 2 from the chapter select.

Chapter 2:

Sequence with the doctor: "The first doctor to look at me was an old man ..."
-> right trigger

Seira: "Wow, Takky! You hate going outside, but you still..."
-> right trigger

Just hit "ok" when you receive the medical formular .

The concert scene with FES: "-looked right at me."
-> right trigger
During the sequence with the doors answer: Yes, no, yes, yes, yes

Skip any decision until you reach the sequence with the doors in chapter 6.
Respond with: Yes, yes, no, no, yes

Feel free to skip until you reach the ending.

"A Bloody Contract for Your Sins" ending unlocked.

Select chapter 3 from the chapter select.

Chapter 3:

At the street: "And then she really swung it!"
-> no trigger
During the sequence with the doors answer: Yes, yes, yes, yes, no

Skip any decision until you reach the sequence with the doors in chapter 6.
Respond with: Yes, yes, no, no, yes

Feel free to skip until you reach the ending.

"Deus Ex Machina" ending unlocked.

Select chapter 3 from the chapter select.

Chapter 3:

At the street: "And then she really swung it!"
-> left trigger

With Misumi inside the school building: "FES didn't even look at him."
-> left trigger

Takumi's room: "Damn it... Not now."
-> left trigger

With Kozue in the class room: "Sure enough, there was a girl there."
-> left trigger
During the sequence with the doors answer: Yes, yes, yes, yes, no

Skip any decision until you reach the sequence with the doors in chapter 6.
Respond with: Yes, yes, no, no, yes

Feel free to skip until you reach the ending.

"A Disease that Leads to Slaughter" ending unlocked.

Start a new game.

Chapter 1:
Answer all three questions with "yes".

With Misumi in the class room: "I hated to disappoint Misumi when he was so excited, but I had no intention of going."
-> no trigger
You'll see a text on the blackboard. The scene then proceeds by showing you two doors, respond to the questions like this: No, no, yes, yes, yes

Skip any decision until you reach the sequence with the doors in chapter 6.
Respond with: Yes, yes, no, no, yes

Feel free to skip until you reach the ending.

"Moon and Sun" ending unlocked.

After unlocking all the endings you'll be able to reach the "Blue Sky" ending through the main menu.
Respond to the questions like this: Yes, yes, no, no, no, yes, yes, yes, yes, yes, yes, yes, yes, yes, yes

By now you should have gotten all the achievements.
It's possible that the tips and CG achievement unlocks after opening the menu and viewing all of them.