Sei Shimai Rena & Tyseria ~Kedakaki Otome no Tamashii wa, Seiin Choukyou no Hate ni Yami o Samayou~

There were girls called 'holy sisters', at church in a small country.

Big sister, Ticeria, served as a healing maiden, and little sister, Lena, served as a protector from evil monsters.

They have been performing their own duties, until Lena's jealous toward her sister led her to cooperate with Sieg the vampire - in order to turn Ticeria into a monster.

Ticeria - who has been captured and violated, still wished for human and monster to co-exist in peace.

Lena - who wants to humiliate her sister, even submits her own body for the monster.

[From DLsite English]