Here is the full list of all 47 Danganronpa 2: Goodbye Despair achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Unlocked all gallery items
Earned every other achievement in the game
Fully raised every type of pet
Hajime Hinata breaks through level 99
Cleared a class trial without using your Concentration skill once
Cleared a class trial without taking any damage
Collected every possible item in Magical Miracle Girl Monomi
Cleared all stages of Magical Miracle Girl Monomi
Saw every possible Island Mode ending
Cleared Island Mode once
Break through 10,000 total number of steps
Collected every possible present
Filled in every page of Peko's Report Card
Filled in every page of every character's Report Card
Filled in every page of Mikan's Report Card
Filled in every page of Ibuki's Report Card
Filled in every page of Mahiru's Report Card
Filled in every page of Hiyoko's Report Card
Filled in every page of Fuyuhiko's Report Card
Filled in every page of Nekomaru's Report Card
Filled in every page of Teruteru's Report Card
Filled in every page of Kazuichi's Report Card
Filled in every page of Byakuya's Report Card
Filled in every page of Nagito's Report Card
Filled in every page of Chiaki's Report Card
Challenged vending machine 100 times
Collected 50 unique presents
Obtained all types of items in vending machine
Finished every chapter
Found every Hidden Monokuma
Collected 999 Monocoins
Finished Chapter 5
Filled in every page of Akane's Report Card
Finished Chapter 4
Destroyed 500 white noise lines across all class trials
Hajime Hinata breaks through level 50
Finished Chapter 3
Found half of the Hidden Monokumas
Filled in every page of Sonia's Report Card
Finished Chapter 2
Cleared a class trial without having to retry once
Destroyed 100 white noise lines across all class trials
Filled in every page of Gundham's Report Card
Finished Chapter 1
Break through 5000 total number of steps
Finished the prologue
Fully raised one type of pet