21: Two One

21: Two One is a visual novel adventure game originally released for PC with adult content which is then ported to Dreamcast.

Story
After losing you mother to an illness, one day you decided to become a doctor and give your best to help other people not go through the same pain and ordeal. Your name is Takuya Kirishima, and you lived up to your expectations and became a skilled surgeon who can perform any surgery without a problem. But patients still die, and you may not be able to save them all… that brings the lack of confidence in you as a doctor and makes you question your goal to become a doctor. Seri Sakaki is a young nurse, and an old childhood friend of yours who is trying to help you deal with your limitations as a human. At such time, a murder occurs at the hospital and people start suffering from an unknown strange disease. The police investigation into it has been launched which yields many suspects and mysteries, and even more questions.

Gameplay
At its core, this is a visual novel adventure which determines the course of the story based on the choices you make. However, you can also set the mood of your character to trusting, normal, or suspicious, which will also affect the course of the game (quite similar to how it was done in Blade Runner). You will also be able to check the human relation chart to see connection between characters, as well as flow chart to see how the game story branched.