Of all Tokyo's backstreets, the most remote await exploration on the city's outlying islands.

The largest and closest of these, Izu Oshima, beckoned to me this spring, a green gem set in an azure sea. I reserved the high-speed Jetfoil from Tokyo Takeshiba Terminal, which I'm told "flies" to Oshima in one hour and 40 minutes, provided the weather behaves.

Wind snaps nautical flags and swipes passenger's hats as I board the Tairyo, which is emblazoned with a giant rising sun, illustrator Ryohei Yanagihara's (1931-2015) jaunty take on Japan's Maritime Self-Defense Force flag.