Here is the full list of all 18 Panty Party achievements.
Collect all elegant panties.
Collect all panties.
Collect all Mystical panties.
Collect all Taoism panties.
Collect all bear panties.
Collect all unpopular panties.
Collect all Panzi-sama panties.
Finish the story mode.
Clear all arcade stages as fast as possible.
Collect all striped panties.
Clear a single arcade route with a highscore.
Clear all arcade stages.
Finish arcade route 6.
Finish arcade route 5.
Finish arcade route 4.
Finish arcade route 3.
Finish arcade route 2.
Finish arcade route 1.