Here is the full list of all 15 Sakura Alien achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Achieve Hiyori's Ending
Achieve Ena's Ending
Achieve the Harem Ending
Not quite a Fairy Tale
Wakey, wakey, kisses and bakey
Let Hiyori show her affection
Let Hiyori share a secret
Hiyori, the batting center champion
Let Ena be Hiyori's Mannquin
Let Ena have a nice bath
Too close for a new met... alien
Enjoy Hiyori's hotpot together
Was that a meteor?
Let Hiyori watch the stars
Good morning, friend!