The icy moon Ilmatar lies on the edge of the known universe. IN  not only is the ubiquitous crackling of ice heard in the dark depths. Deep darkness is teeming with life.
 
 A scientific expedition at the Hitode submarine station explores wonderful life forms as well as ancient local culture. But in the name of civilization, other visitors also come.
 
 The sea under the ice unexpectedly becomes the focal point of the impending intergalactic conflict between the people and the hostile Sholen race. However, it does not belong to any of  them, belongs to the Ilmatharians. It's their sea.