Here is the full list of all 21 East Tower - there are Takashi achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
You've unlocked all of the Achievements!
You've got the Normal Ending!
You've got the Bad Ending!
You've cleared Stage 4 and done a good job!
You've cleared Stage 3 and done a good job!
You've cleared Stage 1 and done a good job!
You've cleared Stage 2 and done a good job!
You've unlocked all of the CGs!
You've got the Love Ending!
You've cleared Stage 7 and done an excellent job!
You've cleared the Love Stage!
You've cleared Stage 6 and done an excellent job!
You've cleared the Past Stage!
I feel stupid, knowing I was only worried because of him
You've cleared Stage 5 and done an excellent job!
It seems that I'm his first love.
You've cleared Stage 4 and done an excellent job!
You've cleared Stage 3 and done an excellent job!
You've cleared Stage 2 and done an excellent job!
You've cleared Stage 1 and done an excellent job!
You've cleared the Prologue!