A man spends thirty years carving a tunnel through solid rock to undo a murder he committed decades earlier. The work itself becomes his only confession. This OVA understands that atonement isn't a feeling or a moment, it's the exact weight of stone removed by your own hands, one strike at a time, until the path you've built outlives you.

A Buddhist monk carries the weight of his past in Edo period Japan. Zenkai once took a life, and he is determined to atone for that crime. Worshipers bound for an important local shrine must climb over dangerous cliffs, and many have fallen to their deaths along the way. Zenkai resolves to give them a safe passage. At 49, with only a hammer and a chisel, he begins cutting a tunnel through the rock by hand, a labor that will stretch across thirty years and run 185 metres. This single-episode drama draws on the legend behind the tunnel known as Ao no Doumon, the story of one man's long, humble work toward atonement.