DoNoR - Onna Tantei Ryoujoku

Futaba Kawana is an attractive American detective, who recently uncovered the whereabouts of her sister, who disappeared in Japan some few years ago. Once she arrives to Japan, Futaba hurries to the hospital where her sister was last seen. The hospital is one of the best hospitals in Japan, but many strange rumors are floating around. People have seen dead people coming back alive, lost people found, and so on. As our heroine searches for clues, she finds out that the hospital is actually a huge whorehouse controlled by some organization. To find out about the organization, our heroine becomes a nurse at the hospital, but...

This game runs on a system called, "The Buddy System." This means that there are multiple characters and multiple scenarios, where each character has it's own story. In order to understand the complete story, you have to go through each character's story. Besides our heroine, you will meet Chiya, Aya, Shihomi, and Mio. Take out your sexual desires on these beautiful but strong girls.

[From Gamelex]