Here is the full list of all 19 Lily's Day Off achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Change Lily's clothes
Find the secret menu!
Check out the game's credits
See the game's true ending
See ending 15 in the game
See ending 14 in the game
See ending 13 in the game
See ending 10 in the game
See ending 9 in the game
See ending 12 in the game
See ending 11 in the game
See ending 8 in the game
See ending 7 in the game
See ending 6 in the game
See ending 5 in the game
See ending 4 in the game
See ending 3 in the game
See ending 2 in the game
See ending 1 in the game