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.
Let Hiyori share a secret
Let Hiyori show her affection
Wakey, wakey, kisses and bakey
Not quite a Fairy Tale
Achieve Ena's Ending
Achieve Hiyori's Ending
Achieve the Harem Ending
Let Hiyori watch the stars
Was that a meteor?
Enjoy Hiyori's hotpot together
Too close for a new met... alien
Let Ena have a nice bath
Let Ena be Hiyori's Mannquin
Hiyori, the batting center champion
Good morning, friend!