Chosan was a planet which was settled by humans. Its two major continents, Calabraxia and Pevana, warred upon each other until Bernice Summerfield stopped the conflict. (AUDIO: The Secret of Cassandra)
About four Chosan years after the war, the Earth Reptile Council placed a Sea Devil colony on the planet. Following this, it was discovered that the native form of life, a sentient protein, could mutate the colonists. (AUDIO: The Poison Seas)