With Dan/Ultraseven weakened and possibly dying the alien invaders ramp up their plan to conquer the Earth. If mankind doesn't surrender billions will die in "The Biggest Invasion in History."
The numerous fights with alien kaiju have finally taken their toll on Dan/Ultraseven as he finds himself sick and weak, his superior demands he return to the Land of Light to recuperate but he refuses as Earth still needs him.
The Terrestrial Defense Force develops a new super-weapon that can destroy a whole planet and when it is tested against a supposedly uninhabited planet Earth soon finds itself facing a very angry space monster.
Ultraseven tries to negotiate peace between Earth and the Alien Pedan, unfortunately the treacherous extraterrestrials only have invasion on the minds.
A race of undersea beings claim to be the "rightful rulers" of the undersea floor, having been driven into the sea by humans eons ago, and now they will fight back against human's further expansion into the sea.