As of writing, there are 35 achievements in the game. Note that there are technically no missable achievements due to the flow chart feature in the game.

The game has a feature that allows you to revisit any part of the story via flow chart. So feel free to play through the game on your own and use this guide to find any remaining achievements.

There will not be any major story spoilers, but there will be names of events mentioned, so it is recommended to use this guide after finishing at least one playthrough.

These are the achievements you will naturally get by progressing the story.

Reverse
Complete Day 1
Reunion
Complete Day 2
Drowning
Complete Day 3
Conflict
Complete Day 4
Family
Complete Day 5
Symbol
Complete Day 6
Chaos
Complete Day 7
Reality
Complete Day 8
Debt
Complete Day 9
Self-Reflection
Complete Day 10
Existence
Complete Day 11
Re-connect
See the truth
Other Story Achievements
Language
Use topic for the first time
Fog
Organize thoughts for the first time
Clarity
Organize all thoughts
Open-ended
Enter Day 12 without obtaining all key topics
Note: You should get this naturally in your first playthrough.

These are the achievements related to endings for the game.

Mirage
Complete Ruo Fengyi's alternate ending
(Day 11 "Best Friends") Stop Ruo Fengyi
Note: If this option does not pop up, you may need this topic: (Day 4 "Request") Agree to write lyrics
Detach
Leave with Su Jingxian
(Day 8 "Confession") Apologize -> Drop everything and take Su Jingxian's hand
Future
Confess your feelings to Su Jingxian
(Day 11 "Answers") Say nothing -> Wait -> See her after the graduation ceremory -> Go find her now
Farewell
Bid farewell to Su Jingxian
(Day 11 "Answers") Say nothing -> Wait -> See her after the graduation ceremory -> Forget it -> Things that I want to say
Malice
Malice
Complete every bad ending
Note: You do not need alternate endings for this achievement.
(Day 1)
"Meet up with Fengyi": Instead of meeting up with Fengyi, go back home.
"Overwritten Memory": Immediately leave the house through the right.
(Day 2)
"Before the Date": Interact with the bed.
(Day 3)
"Old Classroom": Interact with the desk -> Talk to Fengyi -> Leave him alone.
(Day 6)
"Promise": Leave the house without interacting with the landline.
"Hallucination": Tell the truth
(Day 7)
"New World": Interact with the lamp -> Immediately go right and open the door.

These are achievements that do not fit into any above categories, including stuff like collectibles, topics, and easy-to-miss achievements. For topics specifically, you do not need to get every topic in the game for any achievement, but make sure to talk to all the characters that pop up in the top right corner to ensure you can meet any requirements.

Topics
Confusion
Obtain Wu Xiaobo's final topic
(Day 9 "Before Opening the Store") Go outside and talk to Xiaobo.
Boyhood
Obtain Yang Chengcheng's final topic
(Day 11 "Halfway through the Party") Interact with Chengcheng.
Friendship
Obtain Ruo Fengyi's final topic
(Day 11 "Best Friends") Hear him play one last time.
Marriage
Obtain the Couple's final topic.
(Day 11 "Party Prep") Interact with the grocery store.
Record
Obtain every character's journal
Just make sure to talk to all characters that pop up in the top right corner and you should naturally get this achievement. You may need multiple topics for each character that pop up in Baichuan's journal.
Omniscience
Obtain every topic
Note You do not actually need every single topic.
I got this after getting everyone's final topic.
Other Achievements
Rewind
Use the plot chart to start from a story node for the first time
In the menu, click continue and choose to continue from one of the nodes.
Nostalgia
Pick up the WOLFMAN
(Day 1 "Overwritten Memory") Interact with the WOLFMAN
Connect
Examine Ji Qiuyu's journal for the first time
You will unlock Qiuyu's journal near the beginning of the story. Click on it on the top left corner.
Bystander
Talk to every NPC
Make sure to walk around until you see each NPC's text bubbles at least once. I unlocked this on Day 8.
Metaphor
Obtain every card
Note: You only need 12 of the 14 cards
You will likely get this achievement progressing through the story, as most cards are within a story's scenario. Make sure to interact with any sparkles you see in the area.
Well-Wish
Give Owner Lady's gift to Chengcheng
Refer to achievement "Marriage" then go to Day 11 "Halfway through the Party" and give the 4WD to Chengcheng.
Past
See every memory piece
Will unlock as you progress through the story. Make sure to get the "Future" achievement to be safe.
Listener
Listen to every radio broadcast.
Each night before ending the day, interact with the radio to the left of the bed.
Note: You only need to do this 6-7 times.