In the near future, computer and AI technology has advanced to the point where robots and androids live and work alongside humans. However, while war has all but ended, terrorism is on the rise, and in particular, there have been an increasing amount of robot uprisings in recent years. To combat this threat, the government has established strict regulations forbidding any robots capable of emotion.
Yuna Fubuki is the newest intern at Arion Medical Center, a prestigious and advanced medical facility. However, Yuna has a secret: she's actually a highly-advanced android built to be indistinguishable from a real human. She has come to AMC along with her creator, robotics prodigy Souji Saegusa, to put her abilities to the test. She must train and work as a nurse for three months without anyone discovering that she is not actually human. However, AMC holds its own share of dark secrets, and things aren't going to be simple for Yuna.
Medical 91 is a Japanese-style visual novel. The majority of the game is spent reading and listening to the story unfold, though Yuna will often be given choices that will cause the story to branch in varying ways. At many points, it is possible to move freely throughout the hospital to speak with the other characters on numerous subjects, with the story only proceeding once the proper conversations have taken place. There are also certain segments where the player must choose locations to escape pursuit, as well as avoid capture in a timing-based minigame.