Here is the full list of all 22 The Last Sky achievements.
Build the toy plane.
Finish playing the piano.
Get 20 intelligent responses from the Soul Communicator.
Clink the jar.
Light the fireplace.
Blow out the candle.
Solve every star constellation at least once.
Complete the piano puzzle without touching any incorrect white keys.
Complete the piano puzzle without jumping or floating.
Complete the game with the "Nirvana" ending in under 30 minutes.
Burn your note to Juliet.
Read every book on your desk.
Play something on the gramophone.
Examine your ring.
Gain direction from Tarak.
Catch all the fireflies on the lake.
Get through the war without a single fault.
Clean up all your toys.
Knock every book to the floor.
Complete the game with the "Nirvana" ending.
Complete the game with the "Samsara" ending.
Successfully navigate a previously unknown depth of your mind.