Keelung, Taiwan —

You can now fall asleep on a ferry in Taiwan and wake up in Japan.

On the surface, the Yaima Maru offers a perfect slow-travel escape — a passenger ferry equipped with saunas, karaoke rooms and a top-deck cafe.

Launched in Taiwan last month to the sound of drums and a traditional lion dance, the 21,000-ton civilian vessel connects the northern Taiwan port of Keelung with the island of Ishigaki, in southwestern Japan’s idyllic Okinawa prefecture.

But as Beijing ramps up military pressure around Taiwan and Japan shores up its own southwestern defenses, the route has drawn scrutiny — not least because the vessel has been officially earmarked by Tokyo to assist in emergency evacuations if regional tensions erupt into open conflict.