"Tōsōchū: The Great Mission" is a science fiction anime series set in a dystopian future where humanity is under the control of an oppressive regime known as the Galactic Empire. The story centers on a group of rebels, the Tōsōchū, who are determined to overthrow the Empire and restore freedom to the galaxy. The protagonist, Kakeru, is a young pilot who joins the rebellion after his home planet is destroyed by the Empire. Kakeru possesses a unique ability to synchronize with advanced mecha units, making him a key asset in the fight against the Empire.

The narrative unfolds as Kakeru and his comrades embark on a series of missions to weaken the Empire's hold on the galaxy. They infiltrate heavily guarded facilities, sabotage supply lines, and engage in intense space battles. Along the way, Kakeru forms bonds with other members of the Tōsōchū, including Rei, a skilled strategist, and Yuna, a former Imperial soldier who defects to the rebellion. The group faces numerous challenges, including internal conflicts, betrayals, and the constant threat of the Empire's elite forces, led by the ruthless Commander Zane.

As the story progresses, Kakeru discovers that the Empire's control is maintained through a powerful artificial intelligence system known as the Nexus. The Nexus not only governs the Empire's military operations but also suppresses the free will of its citizens. The Tōsōchū's ultimate goal becomes the destruction of the Nexus, which they believe will cripple the Empire and liberate the galaxy. The series builds toward a climactic confrontation between the Tōsōchū and the Empire, with Kakeru's abilities playing a pivotal role in the outcome.

Themes of resistance, sacrifice, and the struggle for freedom are central to the narrative. The characters' motivations and backstories are explored, adding depth to their actions and decisions. The series balances action-packed sequences with moments of character development, creating a compelling and cohesive storyline. "Tōsōchū: The Great Mission" offers a blend of mecha combat, political intrigue, and personal drama, making it a notable entry in the science fiction genre.