Here is the full list of all 20 Hentai Neon achievements.
Pass level 20
Pass level 19
Pass level 18
Pass level 17
Pass level 16
Pass level 15
Pass level 14
Pass level 13
Pass level 12
Pass level 11
Pass level 10
Pass level 9
Pass level 8
Pass level 7
Pass level 6
Pass level 5
Pass level 4
Pass level 3
Pass level 2
Pass level 1