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.
Profess your love for Madeleine.
Profess your love for Daffodil.
Bring the story to a premature close.
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.
Read Daffodil's story.
The traveller refuses to tell Daffodil the truth.
Offer Daffodil a few too many compliments.
Answer Lycrois' question incorrectly.
Let yourself forget everything.
Lycoris gets a little too possessive.
Return to the library for a second time.
Read Madeleine's story.
Madeleine refuses to share her story.
D-Did you just insult a girl's cooking?! You monster!
Throw caution to the wind!
Listen to a mysterious voice.
The traveller leaves the church early.
Start a new story.
Take the traveller's name for your own.
Make yourself the third Madeleine.
Multiply the number of daffodils in the story.
Name yourself after a certain flower.
Try to steal Lycoris' most precious possession.
Lycoris welcomes you to her library.