Here is the full list of all 100 Goddess of Hentai achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Complete 21st portrait on hard
Complete 20th portrait on hard
Undress 5th goddess on hard
Complete 19th portrait on hard
Complete 18th portrait on hard
Complete 17th portrait on hard
Complete 16th portrait on hard
Undress 4th goddess on hard
Complete 15th portrait on hard
Complete 14th portrait on hard
Complete 13th portrait on hard
Complete 12th portrait on hard
Undress 3rd goddess on hard
Complete 11th portrait on hard
Complete 10th portrait on hard
Complete 9th portrait on hard
Complete 8th portrait on hard
Undress 2nd goddess on hard
Complete 7th portrait on hard
Complete 6th portrait on hard
Complete 5th portrait on hard
Complete 24th portrait on easy
Undress 6th goddess on easy
Complete 23rd portrait on easy
Complete 22nd portrait on easy
Complete 21st portrait on easy
Complete 20th portrait on easy
Undress 5th goddess on easy
Complete 19th portrait on easy
Complete 18th portrait on easy
Complete 17th portrait on easy
Complete 16th portrait on easy
Undress 4th goddess on easy
Complete 15th portrait on easy
Complete 14th portrait on easy
Complete 13th portrait on easy
Complete 12th portrait on easy
Undress 3rd goddess on easy
Complete 11th portrait on easy
Complete 10th portrait on easy
Complete 9th portrait on easy
Complete 8th portrait on easy
Undress 2nd goddess on easy
Complete 7th portrait on easy
Complete 6th portrait on easy
Complete 5th portrait on easy
Complete 4th portrait on hard
Undress 1st goddess on hard
Complete 3rd portrait on hard
Complete 2nd portrait on hard
Complete 1st portrait on hard
Complete 4th portrait on easy
Undress 1st goddess on easy
Complete 3rd portrait on easy
Complete 2nd portrait on easy
Complete 1st portrait on easy
Complete 25th portrait on easy
Complete 26th portrait on easy
Complete 27th portrait on easy
Complete 28th portrait on easy
Complete 29th portrait on easy
Complete 30th portrait on easy
Complete 31st portrait on easy
Complete 32nd portrait on easy
Complete 33rd portrait on easy
Complete 34th portrait on easy
Complete 35th portrait on easy
Complete 36th portrait on easy
Complete 37th portrait on easy
Complete 38th portrait on easy
Complete 39th portrait on easy
Complete 40th portrait on easy
Complete 22nd portrait on hard
Complete 23rd portrait on hard
Complete 24th portrait on hard
Complete 25th portrait on hard
Complete 26th portrait on hard
Complete 27th portrait on hard
Complete 28th portrait on hard
Complete 29th portrait on hard
Complete 30th portrait on hard
Complete 31st portrait on hard
Complete 32nd portrait on hard
Complete 33rd portrait on hard
Complete 34th portrait on hard
Complete 35th portrait on hard
Complete 36th portrait on hard
Complete 37th portrait on hard
Complete 38th portrait on hard
Complete 39th portrait on hard
Complete 40th portrait on hard
Undress 7th goddess on easy
Undress 8th goddess on easy
Undress 9th goddess on easy
Undress 10th goddess on easy
Undress 6th goddess on hard
Undress 7th goddess on hard
Undress 8th goddess on hard
Undress 9th goddess on hard
Undress 10th goddess on hard