Story
Prologue:

Our universe is devided into two dimensions-inner space and outer space-that are locked in an eternal power struggle.In order to defeat against outer space,the leaders of inner space have created several planets known as "earths" where they cultivate aggressive life-forms called humans.Humans act as inner space's defensive front line.

However,the inherent emotional instability of humans is the cause of much concern for the leaders of inner space,who are known as the "creators." Every so often,humans will overcome their natural desire to destroy beings different from themselves and chose instead to live in peace.

Each time humans stray from their intended purpose,the creators wipe the planet of it's human population.They then create a new earth and cultivate humanity anew.In wiping out their defensive front line,however,they give outer space an opportunity to launch an assault.

The Girl From Outer Space:

Sensing an oppening in inner space's defences,outer space sent a reconnaissance unit disguised as a human girl to inner space.The girl landed on the planet Earth-4,which had been wiped of human life by the creators.

However,during the process of infiltrating inner space,the recon unit lost her memory.Her directive to investigate and document the weakness of humans grew vague,leaving her merely with a curiosity toward them.She drifted through the desolate ruins of Earth-4,knowing only that she felt compelled to learn more about the human race.

Inner space soon detected the spy from outer space.They sent a rookie operative,Isa Jo,to Earth-4 to destroy the recon unit.This decision sparked much controversy within the ranks of inner space's defence forces,as Isa's father's blood had been tainted by that of outer space,making Isa something not entirely human.