A modern warship slides through a time portal into 1942 and realizes immediately that sinking one ship changes everything. The crew doesn't get to choose between doing nothing and playing god, the moment they arrive, they're already changing history just by existing. Every decision splits into ten worse ones, and the show treats that suffocation like the actual horror it is, not a setup for heroics.

Mirai, an improved Kongou-class Aegis destroyer and one of the newest ships in Japan's Self Defense Force, is out on scheduled training exercises when a violent storm throws its navigation into chaos. Once the crew recovers, they find they have been sent back to June 4, 1942, the day of the Battle of Midway. Under Captain Umezu Saburo and Executive Officer Kadomatsu Yosuke, they stay clear of the fighting and vow to remain unknown, altering the past as little as they can. Then Kadomatsu saves the dying Lt. Commander Kusaka Takumi from the wreck of his Zero as it goes down. Soon the Mirai is pulled into a fight with a U.S. submarine that was never part of history, and the war's course begins to shift. Based on Kawaguchi Kaiji's manga, the series is a time-slip military drama that blends action and science fiction.