Set in the 1700's among the dockyards, after hours underground bare knuckle prize fights take place.
The narrator is told a tale of "SATTO" (if I recollect) the greatest fighter to ever live.
Satto was captured at sea in a fishing net unconscious. None of the crew had ever seen a bi-pedal, web-fingered, scaly, elaborately illustrated skinned creature.
Imprisoned & forced to fight, he used a broken tooth to carve his story in unknown symbols (Japanese).
He was at the epicenter of 1945 Hiroshima drop in a fishing boat and got blasted back in time. He then swam away.