Here is the full list of all 30 Once on a windswept night achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Lycoris gets a little too possessive.
Return to the library when Lycoris needs you the most.
Profess your love for Daffodil.
Profess your love for Madeleine.
Learn Lycoris' favourite flavour of tea.
Answer Lycrois' question incorrectly.
Take the traveller's name for your own.
Make yourself the third Madeleine.
Wait for a play that's already over.
Reach your happy ending.
You remember who you are.
Read a lonely spirit's story.
Multiply the number of daffodils in the story.
Bring the story to a premature close.
Read Daffodil's story.
The traveller refuses to tell Daffodil the truth.
Offer Daffodil a few too many compliments.
D-Did you just insult a girl's cooking?! You monster!
Listen to a mysterious voice.
The traveller leaves the church early.
Name yourself after a certain flower.
Let yourself forget everything.
Return to the library for a second time.
Read Madeleine's story.
Madeleine refuses to share her story.
Throw caution to the wind!
Start a new story.
Try to steal Lycoris' most precious possession.
Lycoris welcomes you to her library.
Arrange the actors back on the stage.