I recently bought the Anfibio Nano RTC, a very affordable watercraft called a packraft, and took it out on Nakagawa River (?????????) for a test spin. This raft is tiny, and it and all of its accessories (ex-paddle) fit completely in one small backpack-like waterproof bag.
Anfibio Nano-RTC in all its glory
Since most navigable waterways and lakes in Japan are open to use by the public for unpowered transits, I figured I would try it on the cheap. This model of raft is suitable really for only slowly moving / flat water, but that covers many stretches of natural rivers, reservoir lakes, natural lakes, and man-made rivers.