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