Here is the full list of all 20 Happiness Drops! achievements.
Degree of difficulty "SuperEasy" is lift a ban.
Degree of difficulty "SuperHard" is lift a ban.
Degree of difficulty "Expert" is lift a ban.
Achieve 10 victories in ENDLESS mode.
Achieve 20 victories in ENDLESS mode.
To achieve 6 chains combo for the first time.
To achieve 10 chains combo for the first time.
Complete the STORY mode with Haruhi.
Complete the STORY mode with Anri.
Complete the STORY mode with Koyuki.
Complete the STORY mode with Sumomo.
Complete the STORY mode with Ibuki.
STORY mode clear with all characters.
STORY mode clear with the difficulty level "Normal".
STORY mode clear with the difficulty level "Hard".
STORY mode clear with the difficulty level "VeryHard".
STORY mode the difficulty "SuperHard" 1 victory.
STORY mode clear with the difficulty level "SuperHard".
STORY mode the difficulty "Expert" 1 victory.
STORY mode clear with the difficulty level "Expert".