Keisai Aoki (1893-1969) was an inmate at the Japanese National Sanatorium Oshima Seisho-en.

Aoki was diagnosed with leprosy at 16, and was admitted to Oshima Seisho-en, where he became a Christian. He chose to live in a private Christian leprosy home, the Kaishun Hospital established by Hannah Riddell in Kumamato. From here, he was sent to Okinawa on an evangelical mission. As he preached the gospel, he saw the devastating suffering of the people and realised that there must be a place for those who suffer from illness, especially leprosy. After much struggle, repeated rejection, and denunciation, Aoki finally managed to have a piece of land on the island of Gayachi set aside. This was the beginning of Okinawa Airaku-en Sanatorium.