"Planzet" is a science fiction anime set in a future where Earth is under threat from an alien species known as the ETs. The story begins in 2033, when humanity first encounters these extraterrestrial beings. The ETs launch a devastating attack, leaving Earth's major cities in ruins and forcing humanity to retreat into underground shelters. In response, the United Nations establishes the Earth Defense Force (EDF) to combat the alien threat.

The protagonist, Hiroshi Kamiya, is a young man who loses his family during the initial ET invasion. Driven by a desire for revenge, Hiroshi joins the EDF and becomes a pilot of the advanced combat mechs designed to fight the ETs. Alongside him is his childhood friend, Akira Satou, who also joins the EDF and becomes a key figure in the battle against the aliens. The narrative explores their struggles, both on the battlefield and in their personal lives, as they grapple with loss, fear, and the moral complexities of war.

As the conflict intensifies, the EDF discovers that the ETs are not merely mindless invaders but possess a complex social structure and advanced technology. The story delves into the ethical dilemmas faced by the human forces, particularly when they uncover the ETs' true motives and the possibility of coexistence. The tension escalates as Hiroshi and Akira are thrust into increasingly dangerous missions, culminating in a climactic battle that tests their resolve and humanity's survival.

The anime also introduces secondary characters, such as fellow EDF pilots and scientists, who contribute to the overarching narrative by providing insights into the ETs' biology and technology. These characters add depth to the story, highlighting the collaborative effort required to face an existential threat. The plot maintains a steady pace, balancing action sequences with moments of introspection and character development.

"Planzet" concludes with a resolution that leaves room for interpretation, addressing themes of sacrifice, resilience, and the potential for understanding between species. The anime's narrative structure and character arcs are designed to engage viewers with its exploration of humanity's response to an unprecedented crisis.