Helter Skelter: Hakudaku no Mura

If you love seeing girls being brutally raped, these hentai anime are for you! 

Both are hentai involving rape and abuse. Mother volunteers to be abused to save the daughter and vice versa. 

Both includes the girls kidnapped and brutally raped with sad ending, maybe. It depends on your perspective. 

similiar plot where beautiful heroine getting gang raped by bunch of man... 

Gang rape ceremonies in both series, women are extremely attractive. 

Very hardcore sex scenes in both series. 

Beautiful women getting raped by multiple men, very hardcore. 

Both series have sad ending and in each of them you can find group of guys having lustful group sex with innocent females. What's important we won't find much BSDM or SM scenes in both titles, so if you liked Hakudaku no Mura give a Saimin Ryoujoku Gakuen go because either of them have similar way of showing sex scenes and their variety.