Angel☆Night ~Yamiyo o Kakeru Tenshi-tachi no Monogatari~

In the miraculous World of Demons, there lived a vampiric count. One day, standing near the statue of the Goddess of Time, the count thought with sadness of everyone's mortal fate; at this moment the God of Death appeared, telling the count he has a visitor in his castle. The visitor turns out to be a succubus named Karuru, who suggests that the count trains two young female demons, Tiris and Emalis, and sends them to the other worlds...

[From Moby Games]