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