Assuming the Katana guy is a trained Samurai warrior, and not some fantasy sword collector who bought a replica katana off the home shopping network, and assuming the Fish monger has cut a few giant tuna on YouTube with his sword and isn’t compensating for a small boat, then the Samurai will most likely win for several reasons, the most obvious being that once caught, Tuna don’t fight back against the sword. So there is no defense technique chapter in a tuna sword manual, and therefore no defense against a Samurai attack. 😄
However, the OP states that the warriors are of equal training and ability. The Tuna sword and katana are very similar in dimensions, but the katana is a weapon that has been perfected over centuries to be able to withstand impacts of bone and other swords, and still perform. The differential hardness of the edge and soft core steels absorbs impact forces to keep it from shattering, and any chips and cracks are further compartmentalized by tempered differences along the length of the Hamon.
The tuna sword may or may not be laminated steel, but is more than likely hardened uniformly throughout. This overall hardness of the tuna sword might be softer than a katana, and if so, then the katana could literally cut into the steel of the tuna sword and still be relatively unharmed. So the longer the fight, the better than chances of the Katana winning and the tuna sword being damaged too much to be effective.
The only situation in my mind where the Katana would lose is if the samurai were Tuna – then the tuna sword would win because if you’ve ever seen them cut the tuna with a swords, its clear that shit is kryptonite for tuna!
😄😄
