In the 25th century, a spaceship carrying 300 people leaves the earth in search of a new world in the solar system, but an unexpected accident occurs. They crash into a black hole which is connected to another universe. The people on the ship are cast adrift in an emergency capsule to a planet called Ismo. The story begins 12 years after they have reached Ismo.

Ismo is a star of the Onam System, which corresponds to the Solar System in our universe. It is the only planet left in the Onam System. The Death Star called Yomi is a comet which regularly approaches the Onam System.