Bismark, a huge robot invented by the best scientific experts on earth, is being stored in one of the Galilean satellites of Juniper, Ganymede. In order to protect the peace of the earth, four youngsters are chosen by the federal government to get Bismark and fight against Deathcula, an evil power in the universe, who contrives to seize the control over the solar system.
Deathcula conducts distractions and invasions using all available means, but the four youngsters cooperate with each other and overcome all the conspiracies and traps Deathcula has set for them. The Four soldiers thrive in a series of the battles due to the experience they gain encountering many people who have great impact on them.