Japan's worst-kept secret surfaces after fifty years of silence, and it doesn't care about your present-day politics. The black cylinder isn't a mystery to solve, it's a reckoning that swallows entire fleets whole. A 2-episode OVA has no time for exposition, so it moves like a depth charge, each revelation colder and deeper than the last.
Fifty years after World War II, a UN investigation team arrives in Antarctica to study strange disturbances plaguing the region. What they discover is far worse than anticipated: a massive black cylinder emerges from the ice, ancient and inexplicable, bringing with it the possibility of catastrophic war. The cylinder belongs to the Atragon, a legendary Japanese submarine that vanished during the final moments of WWII. Its crew has survived in frozen isolation, waiting for orders that never came, their ship powered by technology far beyond what the modern world understands. Now awakened and still operating under old military directives, the Atragon threatens global security. What unfolds is a collision between forgotten history and present-day politics. The UN team must navigate treacherous waters, both literal and diplomatic, as they attempt to communicate with a crew living in the past and prevent an international incident that could reshape global power. Beneath the Antarctic ice lies not just a relic of war, but a reminder that some secrets should stay buried. Action and intrigue mount as old loyalties clash with new realities.