Dark Blue hentai series is based on the game by LiLim Darkness of the same name, which was released on May 25, 2011.
A group of people go to a summer house for a vacation, unaware of the perils they will undergo during their stay. A school doctor who accompanies them plans on blackmailing one of the women in the group as he got hold of her diary. Relationships are blurry and chaos starts when one of them dies. Escaped convicts have entered the vicinity and have destroyed the main bridge, rendering these people unable to escape. Now trapped and scared, what are they going to do?