Here is the full list of all 25 Tower of Waifus 2 achievements.
Watch the opening
Choose wrong 8 answers in the battle
Finish the game with Young Arrogant Hero character
Kill 5 enemies by Sword Man
Dead by attacking the Demon Lord
Dead by a trap
Fail the 1st floor
Dead by a magic beam
Watch the secret ending
Finish the game with Mysterious Knight character
Finish the Epilogue
Defeat and talk to the boss
Enter the 9th floor
Win the 8th floor
Choose correct 8 answers in the battle
Win the 7th floor
Win the 6th floor
Kill 20 enemies
Kill 5 enemies by Knight
Kill 1 enemy
Win the 5th floor
Win the 4th floor
Win the 3rd floor
Win the 2nd floor
Win the first floor