"Submarine 707R" is a science fiction anime series set in a near-future world where global tensions escalate due to the emergence of advanced submarine warfare. The story centers on the crew of the submarine 707R, a state-of-the-art vessel designed to combat a rogue fleet of submarines threatening global peace. The narrative begins with the sudden appearance of the mysterious and technologically superior submarine fleet, led by the enigmatic Captain Red. This fleet begins attacking naval forces worldwide, destabilizing international relations and pushing humanity to the brink of war.

The protagonist, Captain Hayami, is a seasoned naval officer tasked with commanding the 707R. Alongside his diverse crew, including the skilled engineer Lieutenant Commander Kaido and the tactical officer Lieutenant Nanba, Hayami must navigate the complexities of underwater combat and political intrigue. The crew faces numerous challenges, including deciphering the motives behind Captain Red's attacks and uncovering the origins of his advanced technology. As the conflict intensifies, the 707R crew discovers that Captain Red's fleet is not merely a rogue force but part of a larger, more sinister agenda tied to a shadowy organization seeking to manipulate global powers.

The series explores themes of loyalty, sacrifice, and the moral ambiguities of warfare. The crew of the 707R is repeatedly tested, both in battle and in their personal convictions, as they confront the ethical dilemmas of using advanced weaponry and the consequences of their actions. The narrative builds toward a climactic confrontation between the 707R and Captain Red's fleet, revealing the true nature of the conflict and the stakes for humanity's future. Through its focus on strategic naval battles and character-driven drama, "Submarine 707R" presents a compelling exploration of futuristic warfare and the human cost of technological advancement.