After the devastating attack of aliens, mankind has been forced to leave the Earth. Now people live in huge spaceships and aliens are fighting on special furs, the pilot of one of which will be the main and geroy.Tanigaze Nagatowho lived all his life in the depths of a huge spaceship "Sidonia" coincidentally falls on the outer levels, inhabited by people. The captain personally met with him and offers to become a pilot-guard. Just at this moment the ship is approaching the mysterious creature - gauna. What is the role of Nagata in the impending battle with Gaun?