Disaster strikes the first manned spacecraft to survey Saturn when the capsule crashes off the coast of Japan. When Jun and Yuriko go flying in the area over the crash, they run low on fuel and must return to the airfield where they discover a strange, floating blob. They drive it to authorities, but the creature begins to expand at an alarming rate, destroying the car and injuring Ippei. Hovering over Tokyo, it absorbs all energy around it or thrown against it, even the full force of a typhoon. At the suggestion of Professor Naramuru, the UN launches a satellite into orbit, igniting as an artificial sun, to lure Balloonga into space.
「燃料が無い」「風船」という通信を最後に墜落した土星ロケット、サタン1号。その後、万城目たちを襲う、突然燃料が切れるという怪現象。風船怪獣バルンガがあらゆる動力を吸収し無限に膨らんでいく…。
