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.
Return to the library when Lycoris needs you the most.
Bring the story to a premature close.
Profess your love for Madeleine.
Profess your love for Daffodil.
Learn Lycoris' favourite flavour of tea.
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.
Name yourself after a certain flower.
Take the traveller's name for your own.
Multiply the number of daffodils in the story.
Read Daffodil's story.
Offer Daffodil a few too many compliments.
The traveller refuses to tell Daffodil the truth.
Make yourself the third Madeleine.
Try to steal Lycoris' most precious possession.
Let yourself forget everything.
Answer Lycrois' question incorrectly.
The traveller leaves the church early.
Listen to a mysterious voice.
Lycoris gets a little too possessive.
Return to the library for a second time.
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.