Here is the full list of all 20 Star Sky 3 achievements.
They Meet at Last
Path to the Waking World
Dark turned to light
It is uncovered
Together forever
Use it well
Release it
A beautiful thing
A trait passed on
She is watching
The guardian
Water or not
Grow more
Where they roam
Being friendly
Friendship
Free at last
They are precious
A magic gift
Fruit from the tree