Buta no Gotoki Sanzoku ni Torawarete Shojo o Ubawareru Kyonyuu Himekishi & Onna Senshi: Zettai Chinpo Nanka ni Maketari Shinai!! The Animation

That day a country fell. The princess knight Anrietta and the female warrior Helga continue to escape while protecting the prince of the destroyed country. However, the party gets caught by a cowardly trap of a group of bandits. With the prince taken hostage, the two warriors cannot offer any resistance. Their hearts and bodies begin to fall to the depravity as the bandits vent their lust on them without mercy. As the princess knight's heart falls into darkness because of the continuous rapes, in order to make the prince hers, she sells her soul to the devil... (This OVA is based on the erotic game by Erectlip.)