Before starting, note that there are several achievements with unusual requirements:

Two achievements are date-related - one for starting new game on August 3rd and one for finishing the game on January 1st.

Two achievements are day-related - one only unlocks on Monday, Wednesday, Friday, Sunday and one only unlocks on Tuesday, Thursday, Saturday.

Two achievements require playing the previous Chichester games:
https://store.steampowered.com/app/1140430/Welcome_To_Chichester__Episode_0/
https://store.steampowered.com/app/963770/Welcome_To_Chichester_1Redux__The_Spy_Of_America_And_The_Long_Vacation/?curator_clanid=33590224
These are also available for free on the developer's itch.io page: https://triority.itch.io/

Note: I've been recommended by a lot of people to reset the achievements before playing, especially if you've played the previous titles. Find it in: Extra Options > Reset Achievements

• Now start a new game.

New Game !!!
Starting a new game

• Select a gender.
  You'll need to play the game twice, once as each gender. The respective achievement will unlock upon finishing the game.

Complete Game As Female Protagonist
Complete the game as a female protagonist


Complete Game As Male Protagonist
Complete the game as a male protagonist

• Enter a new name for your character.
  Any name that's not the default name will unlock the achievement below.

Enter A Name
Enter a name


Prologue
Complete the prologue

• You'll soon reach the following decision:
  
  The choices are ordered randomly.
  
• Go into History > "I think she is holding up <number> fingers"
  
• Answer with <number>.

Chapter 1
Complete Chapter 1


Chapter 2
Complete Chapter 2


Chapter 3
Complete Chapter 3

• Next decision:
  
  
• Save here.
  Each choice unlocks a different achievement. You can choose one, finish the chapter for the achievement, load save and do the other.

Intervene
Intervene in dispute


Don't Intervene
Let the girls argue


Chapter 4
Complete Chapter 4


Butter Market
Visit the Butter Market


Chapter 5
Complete Chapter 5

• Final decision:
  
  
• Save here.
  Again, each choice unlocks a different ending and achievement.
  
  
  • "Good luck with your lecture !"
    Good luck !
    Cindi goes to her lecture alone
    
    
    
    
  • "Do you mind if I come with you ?"
    True Ending
    Get the true ending
    
    
    
    
  • "Do you really need to go ?"
    If it's Monday, Wednesday, Friday or Sunday:
    Good job !
    Not exactly how things should have turned out, but everyone is happy
    
    
    Otherwise:
    Bad luck !
    Rejected by Cindi
    
    
    
    
  • "I want to drag you into a dark alleyway and strip you !"
    Hentai !
    Be the pervert that Grendel always knew you were
    
    
    
    
  • "Bbbbbbbllluuurrrgggghhhh"
    Blurg !
    Faint at the thought of talking to a girl

End Credits
Watch the end credits

Start a New Game or Extra Options > Scenes > Chapter 1

Play until the first decision with the numbers.

Purposely choose the wrong number.

Die
You seem to be slightly dead

This achievement only works after finishing the game once.

Go to Extra Options > Scenes > Chapter 5

Play through the chapter to the end.
The Good News/Bad News decision doesn't matter.

Spoilers
Cindi doesn't like what she comes across

• Play the "Story Recap" from the main menu.

Recap
Complete the episode recap

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• Go to Extra Options > Developer Notes (might need to finish the game first?).

Dev Notes
A short developer note

---

• Preferences > Skip Unseen Text, After Choices, Transitions all ON
  Turn Text Speed to MAX

Speed Run
Complete the visual novel in 1 minute or less


Any ending in chapter 6 is fine.

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• Download Episode 0 from Steam or itch(dot)io[triority.itch.io] and finish it.
  
• Download Episode 1 from Steam or itch(dot)io[triority.itch.io] and finish it.

• Upon Starting a new game:

Completed Episode 0
Completed Episode 0


Completed Episode 1
Completed Episode 1

---

• If it's August 3rd, start a new game:

Was Released At Least A Year Ago Today !
This game was originally released on the 3rd August 2018 !

• If it's January 1st, finish the game:

New Year
Celebrate the New Year by completing the game

These two achievements were added later, so they get their own section.

Preferences > Frying Pan Animation

• Turn it ON and play a new game through chapter 1 for:

New Frying Pan Sequence
Activate the new frying pan sequence

• Turn it OFF and play a new game through chapter 1 for:

Old Frying Pan Sequence
Activate the old frying pan sequence