Before we start.
Because this guide is a 100% Completion Walkthrough, do read at your own risk. We will be talking about some story achievements as well as boss achievements.
I have tried making this guide as in-depth and as detailed as possible.

Now, lets begin.

These achievements are achievements you cannot miss.
They will pop up every time you complete a certian event, when you finish a chapter or when you found your first collectable.
Lets get these achievements out of the way first.


Rented Rooms, Nightmare Hotels
Finished the Prologue.


Human Beings Can Be Awful Cruel
Finished Chapter 1.


The Mask Was A Thing On Its Own
Finished Chapter 2.


You Merely Broke My Life
Finished Chapter 3.


They Call Us Children And They Treat Us Like Mice
Finished Chapter 4.


This Horror Will Grow Mild
Finished Chapter 5.


An End That Repudiated Optimism And Pessimism Alike
Finished all chapters.


Monokuma Fighter
Defeated your first Monokuma.
You'll come across your first Monokuma in the Prologue. So you should be able to grab this immediately.


Ms. Monoku-Man
Played a MONOKU-MAN machine for the first time.
You'll enter a challenge room in the first chapter. With a Monoku-Man Machine. Simply interact with it and you'll receive this achievement.


Burning Your Bridges
Escaped the collapsing bridge.


Shirokuma Rescue Squad
Rescued Shirokuma.


Secret Base Defenders
Defended the secret base from attack.


Keeping The Ratings Down
Cleared the Motivation Machine event.


A Woman's Battle
Komaru vs. Genocide Jack cleared.


Combat Veteran
Defeated every type of Monokuma.
Every time you meet a new type of Monokuma, you will be forced to kill it before advancing. Making this achievement unmissable.


Found You!
Found your first Hidden Kid.
This one is easy. The game gives you a Hidden Kid when you get the Detect Bullet. So you can snatch this achievement immediately. Making this unmissable.


Back To School
Found your first Reference Book.
You will stumble upon a reference book in Chapter 1. Which nets you this achievements. So many easy achievements!

Oh brother. This one is going to involve a lot of searching around.
I would explain to you where everything is, but that will take all day. Considering there are over 200 different collectables to be found. But you can find all of them using this guide[psnprofiles.com].
However, I will list from the easiest to the hardest to find.


Hit The Lists
Handed over your first Hit List to Hiroko.
Easy. You will be given a Hit List when you go down the elevator in Chapter 1. Just talk to Hiroko when you enter the secret base with Shirokuma. And give it to her. Plain and simple. You can miss this if you didn't talk to Hiroko at all or decide to not give her the Hit Lists.


The Road to Literacy
Found your first book and saw your first bonus conversation.
You should be able to find this in any rooms you don't need to visit. So just ignore your main objective and start exploring. However, you might miss this if you ignore all the sparkles you find in the game.


Ultra Know-It-All Girls
Found all Scrap Notes.
If you have been paying attention to the guide, you should be able to get this easily. If you've missed one, you will need to complete the entire game before you can backtrack to a chapter to grab it.


Socki the Sock
Found every page of the Socki the Sock book.
You will find every page of Socki the Sock easily if you have been following the guide. If not, like before, you will need to complete the game before you can backtrack to any chapter.


Hide-And-Seek Champion
Found all of the Hidden Kids.
Ooh. This one, even with a guide. Might be missable. Because the sparkles for the hidden kids are barely noticeable. Make sure you keep a close eye on the area where the guide tells you the sparkles are.


Your License To Kill Is Revoked
Handed over all Hit Lists to Hiroko.
Even if you've found every hit list in Towa City, you won't be able to give it to Hiroko unless you've replayed the game. So just go to Chapter 5 and talk to her and give her your remaining Hit Lists.


Skill Queen
Found all Reference Books.
This one is the hardest because you also need to get an "A" on every chapter to get every extra reference book it gives you. So this ties in to the Best Partners Forever Achievement. Which is really bloody hard to be honest.

I call these achievements "Grinding Achievements" because they require you to do either something perfectly or something over and over again until you get a certian amount of coins.
These achievements no doubt will take you the most time because of stuff like RNG and retries.
I wish you the best of luck.


A Piggy Bank
Collected 100 Monocoins.
This one is easy, you should be able to grab this through natural progression.


A Vault
Collected 10,000 Monocoins.
This one will take a while. Just keep grinding until you reached 10k Monocoins. You can also tie this achievement in with Monokuma Genocider, Blinged Up and Just Don't Run With Them.


Monokuma Hunter
Defeated 100 Monokumas.
You should get this through natural progression, if you have been shooting Monokumas instead of running away that is.


Monokuma Genocider
Defeated 1,000 Monokumas.
This requires you to do some grinding. Which means a lot of chapter replays. I recommend the second chapter as that has the most Monokumas in the Monokuma onslaught just before entering Towa Tower.


Just Don't Run With Them
Maxed out Genocide Jack's scissors.
If you focus all of your upgrades to Genocide Jack, you should be able to get this achievement pretty easily in your first playthrough.


Shinin'
Found half of the Bling Bullets in the game.
This achievement is not that hard. As half of the Bling Bullets in the game are quite relatively cheap. So you can just buy all of them when you find a shop.


Blinged Up
Found all of the Bling Bullets in the game.
This achievement requires you to buy some of the most expensive items in the game. So a lot of grinding will be required. You require over 16k+ Monocoins to be able to purchase every single Bling Bullets in the game. So.... Good luck!

Redemption
Raised Komaru to level 20.
If you have been shooting Monokumas left and right, you should be able to get this in your first playthrough.


Never Stop Growing
Raised Komaru to max level.
This achievement requires you to max out Komaru's level. Which means, you will need to do a second playthrough. Or just grind in a certain chapter.


Hopeful
Earned a B in every chapter.
If you're able to nab every challenge and every Hidden Kids but die or retry here and there, you should be able to get this on your first playthrough.


Best Partners Forever
Earned an A in every chapter.
This achievement is by far the hardest achievement in the game. Only because it is the achievement that will require you to play this game perfectly. No challenge fails. Found every Hidden Kids. And no retries. What so ever. Thanks to user HyperAije for the clarification. You don't need to do the chapters perfectly. All you need to do is get a score above 260 (possibly 250) in order to get an A. Make sure you save often, as loading a save doesn't count towards a retry. Which deducts your point during the end of the chapter.
Be sure to use a guide to figure out exactly how to beat a challenge.

I hope this guide is useful to your journey in completing Ultra Despair Girls.
One of the better games in the series, in my opinion.
Be sure to give this guide a favorite as well as a like and share it with your friends if they're struggling with an achievement.

It's a shame the Steam version doesn't have a full completion achievement like the PSVita version.
Oh well, maybe Spike will add it later.

Oh yeah, did you guys notice this man in the river? I sure did.