Hoshizora no Babylon -Semarikuru Cosmic Sukebe Onee-sans | 星空のバビロン －迫り来るコズミックすけべおねぇさんズ－

Space century 2068. The population ratio and the age when a man is few overwhelmingly. Solar system Mars near Ganymede station.

Protagonist Amanogawa Ginga that belongs to space flight academy, though the space flight examination was accepted to the colony warship Babylon, it suddenly encounters the attack of the universe monster daughter kozumikkureisu that appears from the opponent of the wormhole. Ginga fight back against original immaturity about the command of the captain. It succeeds in the repulse of the enemy, the crisis was able to endure the emergency.

However, the purposes of kozumikkureisu who has the face that resembles the woman of the person type closely, "copulate with a man of earth human for breeding". In this matter "Valuable human race man" Existence of Ginga is recognized by them, babylon to be attack one after another...