Before dive into the achievements, I will first give a brief introduction of the whole structure of this game because I was overwhelmed by how many sections were locked in the GAME START section after I finished Prologue.

Common route:
Prologue;
Chapter 1-4

Character route:
Limbo/Shu/Helvetica/Mozu/Scarecrow each have one Side A and one Side B
within each Side A, there is a possibility of going into a bad end;
Side B will open if you finish Side A without going into the bad ending;
Limbo has 2 bad ends; others each has 1 bad end.

After finishing each character route, two final chapter will unlock subsequently:
Full Circle;
Auld Lang Syne

After finishing each character route, a special short story of that character will unlock in the EXTRA section:
Meatloaf (Limbo);
Meat Sauce (Shu);
Ceviche (Helvetica);
Chop Suey (Mozu);
Hamburger Steak (Scarecrow);
Chain Smoker (everyone)

After finishing Full Circle and Auld Lang Syne, 6 special short stories will unlock in the EXTRA section:
Joker;
Patent Toll;
One and Only;
Wrong Number;
Interview with S;
Fleeting Joy

(Note that Wrong Number and Interview with S are crossover stories with another game developed by 株式会社文化放送, SideKick!, so there are some unfamiliar faces in those two stories.)

I highly suggest finishing everyone’s route even if some of them aren’t your type, because the two chapters unlocked after that are quite vital for the “wholeness” of the main story and the side characters.

I don’t remember the exact requirements for the first 6 extra stories because I saved the EXTRA for the last even if they were unlocked during my playthrough. But, I vaguely remember the EXTRA being unlocked by this sequence: character-specific EXTRA – all-together EXTRA (Chain Smoker) – first 3 EXTRA – 4-6 EXTRA.
So, I’m very sure about the character-specific EXTRA being unlocked when you finished that character’s route. I might be off a bit, but I think the all-together EXTRA unlocks when you finished everyone’s route; first 3 EXTRA unclock when you finished Full Circle; 4-6 EXTRA unlock when you finished Auld Lang Syne.
Also, I guess the three short stories (Wrong Number; Interview with S; Fleeting Joy) in EXTRA would have the prerequisites of having chosen each and every options during Chapter 1 when Alex asked you “Do you have a theme, something in particular you want to write about?”, because the content of those three short stories were related to the three options you were given for that question.

Some start-up choices, and how to go into the route of a specific character:

In general, the rule is pay attention to the color -- the color appear when you make a choice
Limbo -- black
Shu -- blue
Helvetica -- pink
Mozu -- yellow
Scarecrow -- green
No effect on affection points -- white


Chapter 1

· when Helvetica asked "What impression did I leave on you?"
-- I thought you were handsome. (No effect)
-- I thought you were kind of annoying. (affection point for Shu)
· when Shu saied "People will do a lot when money's involved."
-- Honestly, I need the money. (affection point for Helvetica)
-- Forget money, I want a scoop. (affection point for Mozu)


Chapter 2

· when Scarecrow said "A lot happened, and you moved into a new place all of a sudden, so I figured it was weighing down on you... Or something."
-- You're sweet. (affection point for Scarecrow)
-- You all get along, huh? (No effect)
· when doing the test Prof. Sauli gave you, each choice between Yes/No would affect your affection point with one of the character
For this, refer to the guide by SamCThePotato:
https://gtm.you1.cn/sharedfiles/filedetails/?id=2567441959

Chapter 3

· You'll know whose route you get into in Chapter 3 when naming the cat. The cat will accept the name given by the chosen one.
· Also, it will be your chosen one to be with you when you open the letter which contains the result of Rookies of the Year Award.

· when Mozu and you were at the store, Mozu told you about his little sister. He said "My sister is precious to me, so I swear I'll find her. Which is why I keep looking."
-- The choice here does not affect your affection point with him.


For the choices in the character route, I recommend referring to the helpful guide by RusCSI:
https://gtm.you1.cn/sharedfiles/filedetails/?id=2564341499

I divided the achievements into three categories:

Finish the Plot – you get them when finishing a certain chapter (you might need to make certain choice along the way);
Within the Plot – achievements that unlock during a chapter/episode (you need to make certain choices);
Others – achievements that are not related to the plot directly.

Because the icon of the achievements is related to the chapter content/ending, so I didn't put them here (also because steam automatically makes them ridiculously big in the table cells).




“Finish the Plot” achievements




“Within the Plot” achievements
Note that there are minor spoilers in this table

Other achievements



Note that you might miss one or two archive entries even if you have “playthroughed” all the episodes and extras.
For example, I missed one in Helvetica’s Side A because I chose to call Limbo to supervise Mozu and Scarecrow’s Halloween shopping and that led to a slightly different Halloween dinner and one entry in the archive is about what happened if I called Shu to supervise.
But this problem is relatively easy to solve, you can pinpoint where the missing entry should be based on where the locked entry is in the archive, and just go to that episode from the GAME START section and try different choices.