"Planet With" is a 12-episode anime series that blends science fiction, action, and comedy, centered around themes of conflict, forgiveness, and understanding. The story begins with Souya Kuroi, a high school student suffering from amnesia, living a peaceful life with his unusual companions: a giant cat-like creature named Sensei, a small floating robot named Ginko, and a maid named Nezuya. Their quiet existence is disrupted when a mysterious group of armored warriors, the Nebula Weapons, attacks Earth, claiming to protect the planet from an alien threat.

Souya soon learns that he is connected to the alien race known as the Paladin Empire, which was destroyed by the Nebula Weapons. The Nebula Weapons, led by Generalissimo, are part of an interstellar alliance that seeks to prevent civilizations from advancing to a level where they could threaten the universe. Souya, driven by fragmented memories of his past and a desire to uncover the truth, joins forces with a group of unlikely allies, including his classmates and former enemies, to challenge the Nebula Weapons and their motives.

As the story progresses, it is revealed that the conflict is rooted in misunderstandings and miscommunication between civilizations. The Paladin Empire, despite its destruction, had noble intentions, and the Nebula Weapons' actions are driven by a flawed interpretation of their mission. Souya and his allies work to bridge the gap between humans and aliens, advocating for coexistence and mutual understanding. The narrative explores the complexities of war, the consequences of technological advancement, and the importance of empathy in resolving conflicts.

Key characters include Benika Takamagahara, a skilled fighter and leader of the Earth Defense Force; Nozomi Takamagahara, Benika's younger sister and a cheerful, determined individual; and Haru, a former Nebula Weapon pilot who joins Souya's cause. The series balances intense battles with moments of humor and introspection, creating a dynamic and engaging storyline. By the conclusion, the characters achieve a resolution that emphasizes reconciliation and the potential for harmony between different species and cultures.