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.

Moments after the atomic bomb falls on Hiroshima, a secret Japanese submarine heads into battle against an American counterpart, and both vessels disappear from the historical record. Around fifty years later, a special UN task force goes to Antarctica to look into strange phenomena there. The team soon finds itself menaced by a mysterious black cylinder. This two-episode OVA blends action, adventure, fantasy and science fiction.