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 Markus Sesko has published that vast quantities of Japanese swords were exported to China, and across Monsoon Asia. One presumes that most were utilitarian weapons intended for military use, with koshirae built for combat. Oner sees a considerable number of what resemble iron Katchushi and Tosho guards, embellished in foreign styles. A plausible backstory for this is that tsuba accompanying nihonto imported to China and across maritime SE Asia were modified to appeal to local taste. These hybrid objects were then carried by Portuguese, Dutch, and Chinese merchant mariners back to Japan, where they were used as greeting-gifts, and tokens of good will in business dealings.

Here are a few examples. The nakago-ana are telling, as are the delineated seppa-dai (washer-seat). Chinese sword tangs are rectangular in section, like the Japanese trapezoidal shape. The gold dragons on what appears to be a late Muromachi katchushi tsuba are Sino-Islamic in style, with serpentine bodies, cats' paws instead of claws, bifurcated tails, and furry-heads with long forelocks. These characteristics point to Vietnam, where there were a number of Nihon-machi (Japan towns), such as Hội An, just south of Da Nang.