The tale of a Vietnamese transgender entrepreneur has become the country’s biggest film hit — and sparked domestic debate about whether it plays to stereotypes. But Let Hoi Decide has made waves for another reason: it is co-produced by CJ E&M, the South Korean leisure group, which has burrowed to the heart of the Vietnam market.

CJ’s cinematic coup is part of a stream of Japanese and South Korean investment in the country, amid goodwill that contrasts with the troubled relationship between Hanoi and Beijing. While anti-Chinese rioters ransacked foreign companies in Vietnam last year after maritime skirmishes between the countries, Seoul and Tokyo were quietly brandishing hard money and soft power.

Analysts say the push by the two east Asian economic leaders reflects a dovetailing of commercial and strategic interests that has a broader regional importance. While Hanoi wants to limit its dependence on Beijing, Japan and South Korea wish to tighten their embrace with the 10 countries of the Asean Southeast Asian grouping that are preparing — some say optimistically — to launch a single market of more than 500m people this year.