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.
Complete the game without dying
Complete five acceptance loops
Watch the credits
Complete Acceptance
Complete all levels
Complete Depression
Reach all MindImages
Find the 5 hidden glimmers of hope.
Complete Bargaining
There's more than one route to follow.
Complete Anger
Die 100 times
Complete Denial
Do a successful gravityzone jump
Complete Tutorial
Reach one MindImage