When the monster Gudis destroys Jack Shindo's spaceship and traps him on Mars, an alien giant from Nebula M78 shows up and defeats Gudis. To save Jack Shindo's life, this giant merges with him and gives him a device that allows him to turn into this giant whenever fate calls.

After the merge, Jack Shindo can communicate with this giant through telepathy. He then knew that this giant is Ultraman, a warrior from Nebula M78. Ultraman's mission is to destroy Gudis, the monster who polluted the universe. As Ultraman blows up Gudis's body on Mars, Gudis's cells flew to earth, planning to revive by stealing earth's energy, also creating other monsters. Jack Shindo must use the power Ultraman gave him to protect the earth.

After defeating revived Gudis and other monsters on earth, Jack faced space monster Kilazee. Ultraman uses up most of his energy to sustain himself on earth in this battle, so he left Jack Shindo's body and flew back to his home planet, and earth is finally in peace again.