Here is the full list of all 9 Break Chance Memento achievements.
Found and used all mementos.
Unlocked all CGs.
Seen Yukinari's ending.
Seen Natsume's ending.
Seen Chiaki's ending.
Seen Masaharu's ending.
Seen the secret ending.
Seen the Amamiya brothers ending.
Seen the true bad ending.