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.
Take the traveller's name for your own.
Multiply the number of daffodils in the story.
Name yourself after a certain flower.
Try to steal Lycoris' most precious possession.
Read Madeleine's story.
Throw caution to the wind!
Let yourself forget everything.
Return to the library for a second time.
The traveller leaves the church early.
Start a new story.
Lycoris welcomes you to her library.
Make yourself the third Madeleine.
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.
Lycoris gets a little too possessive.
You remember who you are.
Wait for a play that's already over.
Return to the library when Lycoris needs you the most.
Learn Lycoris' favourite flavour of tea.
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.
D-Did you just insult a girl's cooking?! You monster!
Profess your love for Daffodil.
Profess your love for Madeleine.