Okunoshima, known today as Rabbit Island, draws nearly 200,000 visitors a year to feed thousands of tame, fluffy rabbits in the Seto Inland Sea. But this idyllic paradise was once erased from official maps to hide a classified Imperial Japanese Army facility that produced over six kilotons of mustard and tear gas. This episode confronts that jarring contradiction and how a nation grapples with being both victim and aggressor.

We trace the island's transformation from a quiet community of three fishing families into a secret weapons plant, the deception of teenage workers, and the postwar cover-up enabled by Cold War interest in the research data. We then explore the accidental rebirth as a rabbit sanctuary and the bold decision to build a poison gas museum in the middle of a viral tourist destination.

• How a legal loophole in the  ...