Ane wo Tasukeru Tame Nokosareta Shimai wo Yogosu Haitoku no Hibi | 姉を助けるため残された姉妹を穢す背徳の日々

The protagonist Shinichi Ogura who lost mother when it was young, the family called the mother-in-law and three sisters who were the child from previous marriage was obtained because of father's remarriage. Afterwards, Father and mother-in-law are absence in the work-related matter, every day peaceful by four left people is spent.

However a certain day, Eldest daughter Kasumi is kidnapped, from the criminal "Violate the younger sister if you want to help your elder sister" email arrives. Shinichi who did not believe at first, the picture where Kasumi is restricted is shown, it is mentally cornered. And finally, it is Satomi of the second daughter in form agitated by a criminal, in addition Yuu of third daughter, Shinichi who violates. However Kasumi is not liberated, much more childhood friend Makoto and homeroom teacher Naoko until is involved.

Escalating demand. Shinichi who cannot rely on parents and police, the heart is corrupted while being isolated. This abnormal daily life without being over, do you continue till when?