Up until this point, young Sayuri Nanjo has had to live most of her life in a nun-run boarding school for orphans and away from her parents. That's all about to change when her real father mysteriously comes to get her and finally bring her home.

Two young boys sneak aboard a spaceship and find themselves whisked away to the mysterious planet Terra. There, they encounter Gamera's old foe Gyaos and two female aliens with a taste for human brains. Gamera must save the children and battle the new monster Guiron, whose entire body is a deadly living weapon.