>>121217
The heroines need to be defeated in special locations by special monsters. To be more specific you need to capture them and torture them to death. Here is a guide but I won't give any more hints cause discovery is part of the fun;)
If you want fast necro play this >>121204
https://demonion2.wordpress.com/walkthrough/heroine-capture-list-in-defensive-mode/

https://demonion2.wordpress.com/walkthrough/shukakilostrue-route/