Here is the full list of all 19 To the Edge of the Sky achievements.
Saw through Four's eyes in Chapter 03
Cleared Chapter 07
Book 01 Complete
Cleared Chapter 06
Cleared Chapter 05
Cleared Chapter 04
Chose Zero as your Partner
Chose Nine as your Partner
Wanted Six as your Partner ;)
Chose Three as your Partner
Chose Eight as your Partner
Chose Five as your Partner
Chose Four as your Partner
Cleared All Book 01 Bad Endings
Cleared Chapter 03
Cleared Chapter 02
Cleared Chapter 01
Cleared Prologue
Premium Unlocked