Evidence suggests that around 30,000 years ago, humans made a sea crossing—without maps, metal tools or modern boats—from what is now called Taiwan to some of the islands in southern Japan, including Okinawa. To find out exactly how this crossing was made, a team led by Kaifu performed various simulations and experiments, including the use of physical recreations, to learn the most plausible way this crossing was achieved.

Of the two newly published papers, one used numerical simulations to cross one of the strongest currents in the world called the Kuroshio. The simulation showed that a boat made using tools of the time, and the right know-how, could have navigated the Kuroshio. The other paper detailed the construction and testing of a real boat which the team successfully used to paddle between islands over 100 kilometers apart.