After destroying Earth many years ago, the alien race Gauna has been pursuing the remnants of humanity—which, having narrowly escaped, fled across the galaxy in a number of giant seed ships. In the year 3394, Nagate Tanikaze surfaces from his lifelong seclusion deep beneath the seed ship Sidonia in search of food on the upper levels, only to find himself dragged into events unfolding without his knowledge. When the G...