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