Here is the full list of all 27 Stealing a Monster Girl Harem achievements.
Complete Chapter 27
Complete Chapter 26
Complete Chapter 25
Complete Chapter 24
Complete Chapter 23
Complete Chapter 22
Complete Chapter 21
Complete Chapter 20
Complete Chapter 19
Complete Chapter 18
Complete Chapter 17
Complete Chapter 16
Complete Chapter 15
Complete Chapter 14
Complete Chapter 13
Complete Chapter 12
Complete Chapter 11
Complete Chapter 10
Complete Chapter 9
Complete Chapter 8
Complete Chapter 7
Complete Chapter 6
Complete Chapter 5
Complete Chapter 4
Complete Chapter 3
Complete Chapter 2
Complete Chapter 1