Here is the full list of all 13 Chuusotsu! 1st Graduation: Time After Time achievements.
Complete all achievements in Chuusotsu - 1st Graduation
View the extra scenario
Complete the Game
Finish Proposition 3
Spend a Day at the Beach
Finish Proposition 2
Meet Froit & Yung
Finish Proposition 1
Meet Holo
Meet Koiro
Meet Kokoro
Meet Arara
Meet Arue