Here is the full list of all 16 In Between achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Watch the credits
Complete Acceptance
Complete all levels
Complete Depression
Complete Bargaining
Complete Anger
Complete Denial
Die 100 times
Do a successful gravityzone jump
Complete Tutorial
Reach one MindImage
Complete the game without dying
Reach all MindImages
Complete five acceptance loops
There's more than one route to follow.
Find the 5 hidden glimmers of hope.