Frankie Leung Kai-ha has bought three properties in Japan over the past three years. The latest one, bought just last month, is a four-storey building that he plans to renovate into an Airbnb private lodging.The three investments cost about the same as one medium-sized flat in the expensive urban centre of Hong Kong, where Leung lives. His latest deal also came amid the increasingly volatile trade relations between China and the United States, which threaten to undermine the economics of both…