Full list of all 18 Harem Girl: Nikki achievements. It takes around 0-1 hour to unlock all of the achievements in the base game on Windows.
The base game contains 6 achievements, and there is 1 DLC pack containing 12 achievements.
Set 6 Level 1 Completed
Set 5 Level 1 Completed
Set 4 Level 1 Completed
Set 3 Level 1 Completed
Set 2 Level 1 Completed
Set 1 Level 1 Completed
Set 1 Level 2 Completed
Set 1 Level 3 Completed
Set 2 Level 2 Completed
Set 2 Level 3 Completed
Set 3 Level 2 Completed
Set 3 Level 3 Completed
Set 4 Level 2 Completed
Set 4 Level 3 Completed
Set 5 Level 2 Completed
Set 5 Level 3 Completed
Set 6 Level 2 Completed
Set 6 Level 3 Completed