Here is the full list of all 36 Hentai Two Girls achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Complete level 12-3
Complete level 12-2
Complete level 11-2
Complete level 11-3
Complete level 10-3
Complete level 10-2
Complete level 9-2
Complete level 9-3
Complete level 8-3
Complete level 8-2
Complete level 7-2
Complete level 7-3
Complete level 6-2
Complete level 6-3
Complete level 5-3
Complete level 5-2
Complete level 4-3
Complete level 4-2
Complete level 3-3
Complete level 3-2
Complete level 2-3
Complete level 2-2
Complete level 1-3
Complete level 1-2
Complete level 12-1
Complete level 11-1
Complete level 10-1
Complete level 9-1
Complete level 8-1
Complete level 7-1
Complete level 6-1
Complete level 5-1
Complete level 4-1
Complete level 3-1
Complete level 2-1
Complete level 1-1