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