"Marry me, Sword." With his beloved returning to the prison 30 meters underground, Sen, also known as Seth, proposes marriage in the hope of strengthening their bond...!? It all started when an escaped convict, Erie, and former prison guard, Ronnie, showed up at Seth and Sword's house above ground. Seth felt a sense of crisis about the strange cohabitation of the four of them, but one day he lost contact with Sword...!! Erie's plan for revenge involves the two in an unexpected way, and the stage moves to a prison full of danger.