At first I was wondering where the NTR tag was but I guess since the gangrape was actually a flash back and the male lead wasn't actually emotionally traumatized it's not needed. But overall it has a happy ending.
I just skimmed it but why the NTR tag? From what I've read their don't seem to be any boyfriends or anything. From what I can tell all the girls are sluts in a story with free use and massive orgies.
5/5