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