Here is the full list of all 20 HuniePop achievements. It takes around 30-35 hours to unlock all of the achievements on Windows.
Spend the night with ALL the girls without talking with any of them.
Spend the night with 3 girls without upgrading any of your traits.
Earn a 100% completion rate.
Max out both your Munie and Hunie.
Spend the night with ALL the girls within 18 days.
Spend the night with ALL the girls without failing a single date.
Spend the night with ALL the girls without giving any of them an alcoholic drink.
Spend the night with a girl within 4 days.
Successfully complete 10 dates while in Alpha Mode.
Successfully complete a date with at least 20 Moves remaining.
While on a date, earn 2000 or more Affection in a single move.
Have your first successful date with a girl.
Spend the night with a girl for the first time.
Spend the night with the goddess of love.
Give Kyu ALL the pairs of panties after she asks for them.
Successfully complete 5 dates while in Alpha Mode.
Unlock the secret character Kyu.
Unlock the secret character Momo.
Unlock the secret character Celeste.
Unlock the secret character Venus.