Play the main story by selecting "New Game".
Quite a simple achievement, just start up a new game on the main story and you should have it unlocked almost immediately.

Play the main story on High Speed Mode.
Another simple achievement. Just choose a random speed from the high speed mode, start up a new game and you should have this achievement unlocked.

Worth noting however that you do not have to complete a run with high speed mode in order to get this achievement. Simply starting a run to get the achievement before quitting work wonders.

Reach the basement of the main building in the main story.


Reach the annex in the main story.


Reach the basement of the annex in the main story.


Reach the old building in the main story.


Reach the large cell in the main story.


Reach the end screen of the main story.


These achievements should be relatively easy to get, though if you're struggling with completing the game in general then I'd recommend checking out the 6.23 Walkthrough [aooni.fandom.com]

Clear the main story with rank E.


Clear the main story with rank D.


Clear the main story with rank C.


Clear the main story with rank B.


Clear the main story with rank A.


Clear the main story with rank S.

These achievements can be quite challenging to unlock since it requires a good run on your behalf as you'd ideally need to complete a run with low play time, low amount of steps taken and low amount of deaths.

Play time + Steps
Not all puzzles are treated equally as some puzzles are more important than others, so you should try to only do the puzzles that are important & skip those that aren't. eg: Trying to get the bookmark in Annex Basement is a waste of time since the code for the keypad is the same for all run.
Below is a guide that was also made by me which only feature the important puzzles & their respective codes. Memorising or checking them during your run will ensure that your play time and steps will be cut down severely.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3298305101

Deaths
Be sure to save constantly. Everytime you ended up dead then you should go back to the main menu & load back on the previous previous save file before your death. This will ensure a zero or at the very least a very low amount of deaths.

More info regarding death save scumming:
Death save-scumming is unlike your usual save-scumming. Lets say that you have 3 save files saved up, save file A, B, and C, with save file C being your latest one, your most recent death will overwrite the latest save file, in this case being save file C. Thus when save-scumming to avoid death, you should load up a previous previous save file, in this case being either load up save file A or save file B.

Reach the end screen of the main story without getting a game over once.
This achievement isn't as bad as it sounds as you can save-scum your way to it by going back to the main menu and loading a previous previous save file after each death. Though if you do not feel like doing so, then you should at least know that the achievement only care for the deathless completion of a run, how long said run takes is not being accounted for. Thus you can spend a lot time running away from one side of Earth to another.

More info regarding death save scumming:
Death save-scumming is unlike your usual save-scumming. Lets say that you have 3 save files saved up, save file A, B, and C, with save file C being your latest one, your most recent death will overwrite the latest save file, in this case being save file C. Thus when save-scumming to avoid death, you should load up a previous previous save file, in this case being either load up save file A or save file B.

Reach the end screen of the main story without inputting a password incorrectly once.
Just like with the previous achievement(s), you can save-scum with this as well. Make a save before inputting a password, utilise the codes from Essential Codes/Puzzles guide by trial & error-ing the codes, and everytime the password that you've inputted is wrong, load back to your previous save and try inputting another one. Though if you feel that this is "cheating" then you're free to do the puzzles legitly I suppose.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3298305101

More info regarding the save-scumming for this achievement:
Unlike with the Complete Avoidance achievement which tracks death, inputting a wrong password for this achievement WILL NOT overwrite your latest save file, so in this case lets say you've 3 save files, A, B, and C with C being the save file that you've saved up before inputting any password, then in case of incorrectly inputting a password, you can just load up save file C just fine.

Hide from a blue giant by hiding in a closet in the main story.
Very easy achievement. This achievement is pretty much free assuming you do not skip the closet in the double oni chase scene in Annex Basement, so umm, try to not skip it this time? lol

Get dragged into the bathroom and get a game over in the main story.
Basically, at the start of the game, after picking up the plate shards, immediately head to the left in which afterwards an oni will be shown walking pass through the bathroom door. Repeatedly spam interact on the door until Hiroshi gets in and ♥♥♥♥♥♥♥ dies.

update: Actually you don't necessarily have to immediately go to the bathroom after picking up the plate shard. You just need to do this BEFORE the forced oni encounter in the library (which happens after picking up the key in the library).

View the floor plan in the second floor hallway of the main building in the main story.
Just as stated in the achievement description, go to the 2nd floor of the Mansion at any point of the game & view the floor plan located in between of the 2 doors.

Open the lid of the toilet in the main story.
The toilet is located at the utmost left side of the mansion. Just go there at any point of the game, open up the toilet lid and done.

Take a total of 100 steps across all modes.


Take a total of 500 steps across all modes.


Take a total of 2,000 steps across all modes.


Take a total of 5,000 steps across all modes.


Take a total of 15,000 steps across all modes.

This is kinda just one of those achievements that you'd ended up getting without thinking too much about it, though if you do want to grind it then feel free to do so. I suppose the safest place to grind it would be at the start of the game before going into the library as I don't think that any roaming oni will spawn before going to the library, though feel free to correct me on this.

Shake off a blue giant a total of 1 time across all modes.


Shake off a blue giant a total of 5 time across all modes.


Shake off a blue giant a total of 10 time across all modes.


Shake off a blue giant a total of 20 time across all modes.


Shake off a blue giant a total of 50 time across all modes.

This is also another one of those achievements that you ended up getting without thinking too much about. If you do indeed want to grind it, then just save your game before a confirmed oni encounter (eg: first time entering the library) and load the save everytime you managed to escape from the oni.

See the ending of Ai's Story 1


See the ending of Ai's Story 2


See the ending of Ai's Story 3

Since there is no actual way of knowing how unlock the endings, I'll be referencing the requirements that were listed by this guide: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3297102417

First of all I'd very much recommend trying to do the 2nd ending first as this in turn will let you unlock the S rank achievement & an easier time with ending 1.

Ending 2
After you've painfully collected the 3 items that are scattered through the map (doll head, blue stone, red stone), you're going to try and locate the exit and after successfully locating it, be sure to combine the blue stone & red stone with the doll head, save the game (VERY IMPORTANT) and unlock the door. Ending 2 is now done (assuming that you've it completed under the 4-5 mins threshold, if not then tough luck I guess).

Ending 1
Now that you've the 2nd ending completed, be sure to load back the save that you've made before exiting the door in Ending 2, then wait a bit until the play time hit 10 minutes (just to be safe) before escaping, this will then unlock the 1st ending.
EDIT/UPDATE: According to a comment made by DarkLow

引用自 DarkLow：

Just did Ai's Story Ending 1, you only need over 5 minutes to get the Ending 1! No need the 10 minutes to be safe.
When you hit exactly 5 minute mark, you'll hear a loud lightning strike (I reloaded the save file twice and heard it both times)

I've yet to test this out, though it seems plausible enough that I'm willing to take their words for it.

Ending 3
The 3rd ending is the most complicated of them all. You'll have to find the broken syringe and there are 2 methods of getting it depending on how (un)lucky you are.
1) You will randomly found it laying about on the floor, be sure to pick it up & once you've located the doll head, blue stone, and red stone, combine them together and escape normally, this will unlock the 3rd ending.
2) You'd need to find the piano room in which a safe and a map will be present in the room. I believe that the map & the safe will only spawn once you've collected the rest of the items (doll head, blue & red stones), though I'm not too sure about it. Nontherless, once you've managed to find the piano room, check out the map, take a screenshot of it and ♥♥♥♥♥♥♥ trial & error each of the code on the safe (which is located right besides it). Here you could even just use mine.


just repeatedly try out the combination, eg: 1166, 1177, 1188, and so on until you managed to open the safe as the actual way of trying to figure out the code based off the doll room position might ended up frustrating you further. The achievement does not have any kind of time-restriction, so it really doesn't matter whether you take 50 mins or 5 mins to unlock the 3rd ending.
IF you want to do it legitly though, then you'd have to figure out the code based off the position of the doll room, eg: in my run, the doll room is at 3366. I'd then go to the doll room and try to figure out the location of the piano room based off the map, so say, if the location of my piano room ended up being in 2288, then I'd input 2288 onto the safe.

NOTE: DO NOT use this image that I've shared to determine the actual code in your Ai's Story run. Since the rooms seem to be randomly generated, the doll head & 4488 location in my run should be different than yours. You can use this image to trial & error the safe, but do not assume that the position for both the escape room & 4488 room in my run would be the same as yours.

tl;dr my ending pathing recommendation would either be
ending 2 -> ending 1 -> ending 3
or
ending 3 -> ending 2 -> ending 1
Depending on how (un)lucky you can get with the syringe

Play Ai's Story by selecting "New Game".
Just like our earlier achievement, The Beginning of Fear, just simply start up a new game on Ai's Story and you should have it unlocked almost immediately.

Clear Ai's Story with rank E


Clear Ai's Story with rank D


Clear Ai's Story with rank C


Clear Ai's Story with rank B


Clear Ai's Story with rank A


Clear Ai's Story with rank S

S-ranking this is very painful as the rooms for Ai's Story seem to be randomly generated and you yourself too seem to be spawning in a random room. Nontherless it's still very much doable, albeit very painful. Just spam runs & you'll get it soon enough, though if you can, I'd recommend trying to complete this achievement alongside the Ending 2 achievement since the lower play time requirement of ending 2 will helps a lot with the scoring.
You can try to save-scum but it's usually quite hard to do since you only have 1 save slot and the onis can appear out of thin air, ♥♥♥♥♥♥♥ over your runs, good luck.

Obtain the broken syringe in Ai's Story.
You should have this unlocked if you've already unlocked Ending 3. Just as stated before, the syringe can either be found laying on the floor or in the safe, thats about it.

1) 6.23 Walkthrough of Ao Oni[aooni.fandom.com]
2) Steam guide listing off only the essential codes & puzzles
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3298305101
3) YouTube video showcasing tragedy/brutal death

4) Steam guide listing the requirement for Ai's Story endings
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3297102417

Thanks for reading through the guide, If you have any tips that you want to give out or want to point out any mistakes that I might have made in this guide, then feel free to do so via the comment section.